Automated laser workstation for high precision surgical and industrial interventions

ABSTRACT

A method, apparatus and system for template-controlled, precision laser interventions is described that greatly improves the accuracy, speed, range, reliability, versatility, safety, and efficacy of interventions such as laser microsurgery, particularly ophthalmic surgery, and industrial micromachining. The instrument and system are applicable to those specialties wherein the positioning accuracy of laser lesions is critical, wherever accurate containment of the spatial extent of a laser lesion is desirable, and/or whenever precise operations on a target or series of targets subject to movement during the procedure are to be effected. A key object of the present invention is to implement a fully integrated approach based on a number of different instrumental functions all operating in concert within a single, fully automated unit. Each of the complementary, and at times competing, functions requires its own technologies and corresponding subassemblies. The system includes a user interface, wherein the user can either draw, adjust, or designate particular template patterns overlaid on a live video images of the target (such as the cornea) and provide the means for converting the template pattern into a sequence of automatic motion instructions to direct a laser beam to focus sequentially on a number of points in three dimensional space which will, in turn, replicate the designated template pattern into the corresponding surgical or industrial site. The user interface also continuously presents three dimensional visual information to the surgeon/user during the operation, as to the surrounding features of the subject tissue, the topography of the surface to be operated upon or below said surface at a prescribed depth, and as to the precise aiming location and depth of penetration of the treatment laser beam. The system thus comprises the following key elements: (1) a user interface, consisting of a video display, microprocessor and controls,(2) an imaging system, which may include a surgical video microscope with zoom capability, (3) an automated 3D target acquisition and tracking system that can follow the movements of the subject tissue, for example an eye, during the operation, thus allowing the surgeon/user to predetermine his firing pattern based on an image which is automatically stabilized over time. Tracking is considered a critical element of the system designed not only to diagnose, but to also select treatment, position the treatment beam and image the tissue simultaneously with the treatment, while assuring safety at all times, (4) a laser, with which can be focused so that only the precise lesions described by the user interface are effected. The laser parameters are selected to allow execution of the desired procedure at a high rate of independently targeted shots per second, as well as tuning to selectively generate photodisruption of tissues, or photocoagulation as desired, (5) a diagnostic system, incorporating a mapping and topography means for measuring precise surface shapes prior to and subsequent to a procedure, said measurements to be executed on-line within time scales not limited to human response times, and (6) a fast reliable safety means, whereby the laser firing is interrupted automatically, should any conditions arise to warrant such interruption of the procedure.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] The present application is a continuation patent application ofand claims the benefit of priority from U.S. patent application Ser. No.09/543,840 filed Apr. 5, 2000, which is a divisional of U.S. patentapplication Ser. No. 08/523,738 filed Sep. 5, 1995 (now U.S. Pat. No.6,099,522); which is a continuation of Ser. No. 07/843,374 filed Feb.27, 1992 (now abandoned); which is a continuation-in-part of Ser. No.07/307,315 filed Feb. 6, 1989 (now U.S. Pat. No. 5,098,426); and acontinuation-in-part of Ser. No. 07/475,657 filed Feb. 6, 1990 (nowabandoned), the full disclosures of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

[0002] The invention relates to methods and apparatus for performingprecise laser interventions, and in particular those interventionsrelevant to improved methods and apparatus for precision laser surgery.In one preferred embodiment, the system of the invention is used foreffecting precise laser eye surgery. In other embodiments the inventionis applicable to non-surgical diagnostic procedures or non-medicalprocedures involving precision laser operations, such as industrialprocesses.

[0003] When performing laser interventions, whether in medical surgery,industrial processes, or otherwise, several fundamental considerationsare common to most applications and will influence the viability andeffectiveness of the invention. To influence the outcome of theintervention, the present invention addresses both the technicalinnovations involved in an apparatus to facilitate precision laserinterventions, and the methods by which a user of such apparatus canachieve a precise result.

[0004] The present invention addresses the following considerations: (1)how does the user identify a target for the laser intervention, (2) howdoes the user obtain information as to the location and other pertinentfeatures of the target and its important surroundings, (3) how does theuser lock onto that target so that the user has the assurance he isaffecting the intended target, (4) how does the user localize the effectto the target site, (5) how does the user treat a large number ofindividual targets, whether continuously connected, piecewise connected,or disconnected, (6) how does the user assess the effect of theintervention, (7) how does the user correct errors committed eitherduring the course of the intervention or as a result of previousinterventions, (8) how does the user react to changing conditions duringthe course of the intervention to ensure the desired result, and (9) howis safety ensured consistent with U.S. Food and Drug Agency regulationsfor medical instruments and good commercial practice guidelines forindustrial applications.

[0005] Of particular interest are medical interventions such as surgicalprocedures described by Sklar et al. (U.S. Pat. No. 5,098,426 and U.S.patent application Ser. No. 475,657 (now abandoned), which areincorporated herein by reference). Although many different kinds ofsurgery fall within the scope of the present invention, attention isdrawn to corneal refractive surgery in ophthalmology for the treatmentof myopia, hyperopia, and astigmatism.

[0006] For corneal refractive surgery, the above nine considerationsreduce to the following objectives (in accordance with the presentinvention described below): (1) identify the location on or in thecornea to be treated, (2) assure that the target is at the desireddistance from the apparatus, determine the topography of the cornea, anddetermine the location of sensitive tissues to be avoided, (3) identify,quantify, and pursue the motion of suitable part of the cornea which canprovide a reference landmark that will not be altered as a result of thesurgical intervention and, likewise, the depth of variations (forexample, distance form the corneal surface to the front objective lenschanging due to blood pressure pulses) of the corneal surface withrespect to the apparatus such that said motions become transparent tothe user of the apparatus, (4) provide a laser beam which can be focusedonto the precise locations designated by the user such that peripheraldamage is limited to within the tolerable levels both surrounding thetarget site and along the laser beam path anterior and posterior to thetarget site, (5) provide a user interface wherein the user can eitherdraw, adjust, or designate particular template patterns overlaid on alive video image of the cornea and provide the means for converting thetemplate pattern into a sequence of automatic motion instructions whichwill traverse the laser beam to focus sequentially on a number of pointsin three dimensional space which will in turn replicate the designatedtemplate pattern into the corresponding surgical intervention, (6)assure that items (1)-(3) above can be performed continuously during thecourse of and subsequent to the surgery to monitor the evolution of thepertinent corneal surface and provide a means of accurate comparisonbetween pre-operative and post-operative conditions, (7) ensure that thestructural and physiological damage caused by the surgery to the patientis sufficiently small to permit continued interventions on the same eye,(8) automate the interaction between the various components so thattheir use is transparent to the user and so that sufficiently fastelectronics accelerate completion of the surgical intervention withinpre-selected error tolerances, and (9) provide dependable, fail-safesafety features of sufficiently short reaction times to prevent anychance of injury to sensitive corneal tissues. With these objectivesfulfilled, the speed of surgery will no longer be limited by humanperception delay and response times but by the capability of theapparatus to recognize changing patterns and adjust to the newconditions. Equally important, the accuracy of the surgery will not beconstrained by the bounds of human dexterity, but by the mechanicalresolution, precision, and response of advanced electro-optical andelectromechanical systems.

[0007] There are substantial number of different functions which theapparatus of the present invention addresses. Each of the complementaryand at times competing, functions requires its own technologies andcorresponding subassemblies. The present invention describes how thesevarious technologies integrate into a unified workstation to performspecific interventions most efficaciously. For example, for cornealrefractive surgery, as per (1) and (2) above, identify the location tobe treated on or in the cornea, the surgeon/user would use a combinationof video imaging and automated diagnostic devices as described in Sklaret al. (U.S. Pat. No. 5,098,426 and U.S. patent application Ser. No.475,657 (now abandoned)), depth ranging techniques as described inFountain (U.S. Pat. No. 5,162,641), surface topographical techniques, asdescribed in Sklar (U.S. Pat. No. 5,054,907) together with signalenhancement techniques for obtaining curvatures and charting thecontours of the corneal surface as described by McMillan and Sklar (U.S.Pat. No. 5,170,193), profilometry methods as disclosed by McMillan etal. (U.S. Pat. No. 5,283,598), image stabilization techniques asdescribed by Fountain (U.S. Pat. No. 5,162,641), which may all becombined using techniques as described by Sklar et al. (U.S. Pat. No.5,098,426 and U.S. patent application Ser. No. 475,657 (now abandoned)).All of the above listed patent applications and the patent of Fountain(U.S. Pat. No. 5,391,165) are herein incorporated by reference.

[0008] Aspects of the above-referenced disclosures are further used toprovide means of satisfying the key aspects (3)-(9) noted above, such asverification of target distance from the apparatus, tracking the motionof the cornea in three dimensions, providing a laser whose parameterscan be tuned to selectively generate photodisruption of tissues orphotocoagulation as desired, automatically targeting and aiming thelaser beam to precise locations, and supplying a surgeon/user with arelatively simple means of using the apparatus through a computerinterface.

[0009] It is well known that visible light, which is passed withoutsignificant attenuation through most ophthalmic tissues, can be made tocause a plasma breakdown anywhere within eye tissue whenever the laserpulse can be focused to sufficiently high irradiance and fluence levelsto support an avalanche process. The ensuing localized photodisruptionis accomplished by using a strongly focused laser beam such that only inthe immediate focal zone is the electric field sufficiently strong tocause ionization and nowhere else. By using short pulses of controllablysmall laser energy, the damage region can be limited in a predictablemanner while still guaranteeing the peak power necessary for localizedionization. 1101 Furthermore, was lasers of increasingly higherrepetition rate becoming available, the sometimes intricate patternsdesired for a given surgical procedure can be accomplished much fasterthan the capabilities of a surgeon manually to aim and fire recursively.In prior systems and procedures, the surgeon would aim at a target,verify his alignment, and if the target had not moved, then fire thelaser. He would then move on to the next target, and repeat the process.Thus, the limiting factor to the duration of the operation under theseprior procedures was the surgeon's reaction time while he focused on atarget and the patient's movement while the surgeon found his target andreacted to the target recognition by firing the laser. In practice, asurgeon/user can manually observe, identify, move the laser focus toaim, and fire a laser at not more than two shots per second.

[0010] By contrast, a key object of the instrument and system of thepresent invention is to stabilize the motion of the patient by use of anautomated target acquisition and tracking system which allows thesurgeon to predetermine his firing pattern based on an image which isautomatically stabilized over time. The only limitations in time withthe system of the present invention relate to the repetition rate of thelaser itself, and the ability of the tracking system to successfullystabilize the image to within the requisite error tolerances for safetyand efficacy, while providing a means to automatically interrupt laserfiring if the target is not found when a pulse is to be fired. Thus,where it would take several hours for a surgeon/user to execute a givennumber of shots manually (ignoring fatigue factors), only a few minuteswould be required to perform the same procedure when automaticverification of focal point position and target tracking are providedwithin the device.

[0011] It is an object of the present invention to accommodate the mostdemanding tolerances in laser surgery, particularly eye surgery but alsofor other medical specialties, through a method, apparatus and systemfor high-precision laser surgery which provides the surgeon “live” videoimages containing supporting diagnostic information about depth andposition at which a surgical laser will be fired. In a computer, thefull information content of a given signal is interpreted so as toprovide this supporting diagnostic information, and the resultingaccuracy achievable is within a few human cells or better.

[0012] The system, apparatus and method of the present invention forprecision laser surgery, particularly ophthalmic surgery, take a fullyintegrated approach based on a number of different instrumentalfunctions combined within a single, fully automated unit. For example,previous conventional diagnostic instruments available to the ophthalmicsurgeon have included several different apparatus designed to providethe surgeon/user limited measurement information regarding the cornea ofthe eye, such as the corneoscope, the keratometer, and the pachometer.The corneoscope provides contour levels on the outer surface of thecornea, or corneal epithelial surface, derived, typically, fromprojected concentric illumination rings. The keratometer gives crosssectional curvatures of the epithelial surface lens of the eye—thecorneal epithelium surface. Only one group of points is examined, givingvery limited information. Pachometers are used to measure the centralaxis thicknesses of the cornea and anterior chamber.

[0013] The diagnostic functions fulfilled by these devices areinstrumental to characterizing the subject tissue in sufficient detailto allow the surgeon/user to perform high precision ophthalmic surgery.Unfortunately, these and other similar instruments require considerabletime to operate. Further, their use required near-total immobilizationof the eye or, alternatively, the surgeon/user had to be satisfied withinherent inaccuracies; the immobilization methods thus determined thelimitations on the accuracy and efficacy of eye surgery. Nor did thedifferent apparatus lend themselves to being combined into one smoothlyoperating instrument. For all of the above reasons, operation at timescales matched to the actual motions of the tissues targeted for therapyand/or limited by the fastest human response times to those motions(“real time”) has not been possible with any of the conventionalinstruments used to date.

[0014] By contrast, the methods and apparatus disclosed herein, aim toincorporate a mapping and topography means for reconstructing thecorneal surface shape and thickness across the entire cornea. It isfurthermore within the scope of the present invention to provide suchglobal measurements of the corneal refractive power without sacrificinglocal accuracies and while maintaining sufficient working distancebetween the eye and the front optical element of the instrument(objective lens), said measurements to be executed on-line within timescales not limited to human response times. Most standard profilometrytechniques were judged inadequate per the above requirements, requiringcompromises in either accuracies of the computed curvatures (such as,e.g., standard ‘k’ readings of keratometers), speed and ease ofoperation (scanning confocal microscopes) or left no working distancefor the ophthalmologist (corneoscopes and keratoscopes based on “placidodisk” illumination patterns). It is therefore a key objective of thepresent invention to include a new topography assembly that can overcomethe limitations of existing instruments while combining, on-line, and ina cost effective manner, many of the functions of conventionaldiagnostic instruments presently available to the surgeon, as anintegral part of a complete surgical laser unit.

[0015] In one embodiment of the present invention, the cornealrefractive power is measured using a unique projection and profilometrytechnique coupled with signal enhancement methods for surfacereconstruction as disclosed by McMillan and Sklar in U.S. Pat. No.5,170,193 and further extended in larger corneal cross-sections viatechniques described in McMillan et al in U.S. Pat. No. 5,283,598, bothincorporated herein by reference. In another embodiment, digitized slitlamp video images are used to measure the local radii of curvatureacross the entire corneal surface as well as the thickness of thecornea, with no built-in a-priori assumptions about the corneal shape.Both embodiments of the topography system benefit greatly from theavailability of 3-D tracking capability contained within the apparatus.The feature allows elimination of many of the errors and ambiguitiesthat tend to compromise the accuracy of even the best currentlyavailable instruments utilizing fine point edge extraction and advancedsurface fitting techniques. With the computerized topographic methods ofthe present invention, surfaces can be reconstructed (and viewed in 3-D)with accuracies that go well beyond the approximate photokeratometricand pathometry readings as advocated by L'Esperance (U.S. Pat. No.4,669,466), or even the more sophisticated (but complex) corneal mappingmethods as disclosed by Bille (U.S. Pat. No. 5,062,702) and Baron (U.S.Pat. No. 4,761,071).

[0016] While tissue topography is a necessary diagnostic tool formeasuring parameters instrumental to defining templates for the surgery(e.g., refractive power), such instrumentation is not conducive to useduring surgery, but rather before and after surgery. Also, theinformation thus obtained is limited to those parameters characteristicof surface topography (such as radii of curvature of the anterior and/orposterior layers of the cornea or lens). Yet, in many cases, it isdesirable to simultaneously image the target area and deposit laserenergy at a specific location within the tissue itself. To allowreliable, on-line monitoring of a given surgical procedure, additionalmapping and imaging means must therefore be incorporated. The imagingmeans is intended to record, in three-dimensions, the location ofsignificant features of the tissue to be operated upon, includingfeatures located well within the subject tissue. It is therefore anotherobject of the present invention to provide continuously updated videoimages to be presented to the surgeon/user as the surgery progresses,said images to be produced in a cost effective manner yet compatiblewith high resolution and high magnification across a large field of viewand at sufficiently low illumination levels to prevent any discomfort tothe patient.

[0017] The imaging system, or the surgical microscope, requires viewingthe reflected light form the cornea, which has two components: (a)specular (or mirror) reflection from a smooth surface, which returns thelight at an angle opposite the angle of incidence about the normal fromthe surface and also preserves the polarization of the incident beam,and (b) diffuse reflection, in which light returned from a rough surfaceor inhomogeneous material is scattered in all directions and loses thepolarization of the incident beam. No surface or material is perfectlysmooth or rough; thus all reflected light has a specular and a scatteredcomponent. In the case of the cornea there is a strong specularreflection from the front surface/tear layer and weak scattered lightfrom the cellular membranes below. Various standard ‘specularmicroscopes’ have been used to suppress the front surface reflection. Wehave chosen a combination of techniques: some aim at observing thecombined reflections without differentiating between specular or diffusesignals (for operations at or in immediate proximity to the surface ofthe cornea); in others the surface is illuminated with polarized light,with the reflected images then microscopically viewed through a crossedpolarizer for operation within deeper layers, after selectivelyfiltering the more anterior reflections. A rejection of the polarizedcomponent can thus be achieved, greatly enhancing resolution at lowenough light levels to prevent any discomfort to the patient. In eitherembodiment, the imaging system contained within the apparatus of theinvention represents a significant improvement over standard “slit lamp”microscopes such as are in use with most ophthalmic laser systems.

[0018] Other efforts at imaging the eye, such as performed withHeidelberg Instrument Confocal Microscope, or as described by Bille(U.S. Pat. No. 4,579,430), either do not lend themselves to inclusion aspart of an on-line, cost effective, integrated surgical system (for theformer), or rely upon scanning techniques which do not capture an imageof the eye at a given instant in time (for the latter). The method ofthe present invention benefits from having an instantaneous full imagerather than a scanned image; for full efficacy, the method does,however, require that the targeted area be stabilized with respect toboth the imaging and the laser focal region, so as to enhance theaccuracy of laser deposition in tandem with the viewing sharpness.

[0019] Tracking is therefore considered a critical element of a systemdesigned onto only to diagnose, but also select treatment, position thetreatment beam and image the tissue simultaneously with the treatment,while assuring safety at all times. In the case of corneal surgery,movements of the eye must be followed by a tracking system and, suingdedicated microprocessors, at closed-loop refresh speeds surpassingthose achievable by unaided human inspection, by at least an order ofmagnitude. Tracking by following the subject eye tissue, i.e.,recognizing new locations of the same tissue and readjusting the imagingsystem and the surgical laser aim to the new location, assures that thelaser, when firing through a prescribed pattern, will not deviate fromthe pattern an unacceptable distance. In preferred embodiments of theinvention, this distance is held within 5 μm in all situations duringophthalmic surgery, which sets a margin of error for the procedure. Itis possible that with future use and experimentation, it may be foundthat either more stringent or alternatively more lax displacement errortolerances are desirable to improve overall system performance.

[0020] Stabilization of a moving target requires defining the target,characterizing the motion of the target, and readjusting the aim of theapparatus of the present invention repeatedly in a closed-loop system.To meet accuracy goals also requires that the moving parts within theapparatus not contribute internal vibrations, overshoots, or othersources of positioning error which could cumulate to an error in excessof the prescribed dispositioning tolerances. There have been severalprevious attempts at achieving this result. Crane and Steel (AppliedOptics, 24, pp. 527, 1985) and Crane (U.S. Pat. No. 4,443, 075)described a dual Purkinje projection technique to compare thedisplacement of two different-order Purkinje projections over time, anda repositioning apparatus to adjust the isometric transformationcorresponding to the motion. The tracking methods disclosed therein arebased on a fundus illumination and monitoring device that aspires todistinguish translational from rotational eye movements, thusstabilizing an illuminating spot on the retina. However, localization ofthe Purkinje points can be influenced by transient relative motionsbetween the various optical elements of the eye and may providesignificantly fictitious position information for identifying thesurface of the cornea. Motility studies as described by Katz et al.(American Journal of Ophthamology, 107: 356-360, “Slow Saccades in theAcquired Immunodeficiency Syndrome”, April 1989) analyze thetranslations of an image on the retina from which the resultingcoordinate transformation can be computed and galvanometric drivenmirrors can be repositioned. In addition to the fictitious informationdiscussed above due to relative motions between different layers of theeye, the galvanometer drives described by Katz usually are associatedwith considerable overshoot problems. Since saccades can be described ashighly accelerated motions with constantly changing directions,overshoot errors can easily lead to unacceptable errors.

[0021] Bille et al. (U.S. Pat. No. 4,848,340) describes a method offollowing a mark on the epithelial surface of the cornea, supposedly inproximity of the targeted surface material. However, in one of the usesof the present invention, a mark made on the epithelial surface wouldchange its absolute location due to changes in the structure and shapeof the material, caused by use of the instrument itself rather than byeye motions. Therefore, a target tracking and laser positioningmechanism that relies on a mark on the surface of the cornea in order toperform corneal surgery such as described by Bille's tracking methodwould be expected to lead to misdirected positioning of laser lesionsbelow the surface when combined with any suitable focused laser, asintended in one of the uses of the present invention. Moreover, one ofthe features of the present invention is to be able to perform surgeryinside the cornea without having to incise the cornea. The mainadvantages of such a procedure are in avoiding exposure of the eye toinfection and in minimizing patient discomfort. It would hence becounterproductive to mark the surface of the cornea for the purpose offollowing the motion of said mark. In another embodiment taught by Billeet al, the tracking is based on a reference provided by either on theeye's symmetry axis, or the eye's visual axis, with an empiricallydetermined offset between the two. Tracking is then accomplished bymonitoring the reflection form the apex of the cornea, thus avoiding theneed to mark the eye, and/or rely solely on patient fixation. However,with this technique, as in the preferred embodiment taught by Bille etal., the tracking does not follow tissue features generally at the samelocation as the targeted surgical site on or inside the eye. Instead,Bille et al's techniques track reference points that are, in all cases,separate, remote from and may be unrelated to the targeted surgicalsite. Such methods compromise accuracy of tracking in direct proportionto the degree of their remoteness relative to the surgical site.Therefore, they do not adequately provide for the fact that the eye is aliving tissue, moving and changing shape to some extent constantly.Tracking a single point on the cornea, when the cornea itself actuallyshifts considerably on the eye, thus cannot be expected to reflectpositional change of the targeted surgical site.

[0022] By contrast, in the preferred embodiment of the present inventionthe tracking information is obtained through means contiguous to thetarget region, which is mechanically and structurally considered as partof the cornea, but is unlikely to be affected by the course of thesurgery and can thus provide a significant representation ofnon-surgically induced displacements. This is a critical feature of thetracking method disclosed herein, in that involuntary motions of the eye(such as are caused by blood vessel pulsing) can now be accuratelyaccommodated, unlike techniques that rely on remote reference points.

[0023] The accuracy of the apparatus and system of the inventionpreferably is within 5 μm, as determined by a closed-loop system whichincorporates actual measurement of the target position within the loop.(For example, a microstepper motor based assembly may have a single stepresolution of 0.1 μm verified against a motor encoder, but thermalgradients in the slides may yield greater variations. Moreover, positionof the slide can be verified via an independent optical encoder, but therandom vibrations of the target can invalidate the relative accuracy ofthe motor.) Thus, the surgeon has knowledge of the shape of tissueswithin the field of view and the precise location of where he is aimingthe instrument within those structures, to an accuracy of 5 μm. Suchprecision was not attainable in a systematic, predictable manner withany of the prior instruments or practices used. The present inventionthus seeks to obviate the need for binocular vision used to obtainstereoptic images in some prior methods (see., e.g., Crane, U.S. Pat.No. 4,443,075).

[0024] In a preferred embodiment of the invention, the instrument alsoensures that a laser pulse is fired only upon command of thecomputerized controller and after the system has verified that thetracking assembly is still locked onto the desired location, that theenergy being emitted by the laser falls within prescribed errortolerances, and that the aiming and focusing mechanisms have reach theirrequested settings. There is no need to separate aiming beam. In oneembodiment of the present system, the method of parallax ranging isimplemented to map out surfaces posterior to the cornea, but precedingactual treatment.

[0025] Safety is a very important consideration with laser surgery. Inprior surgical systems and procedures, some safety shut-off proceduresfor laser firing have depended upon human reaction time, such as the useof a surgeon's foot pedal for disabling the instrument when a situationarises which would make firing unsafe. In ophthalmology, someinstruments have relied as a safety feature on a pressure sensor locatedwhere the patient's forehead normally rests during surgery. Ifinsufficient pressure were detected by the sensor, the instrument wouldbe disabled from firing.

[0026] Such prior safety systems have inherently had slow reactiontimes, and have not been able to react quickly enough to all of thevarious problems which can arise during a firing sequence. This is acritical concern in ophthalmic surgery, especially where specificsurgical procedures are to be performed near sensitive non-regenerativetissues, such as the corneal endothelium layer and the optic nerve. Incontrast, the target capture and tracking system of the presentinvention makes available a new and highly dependable safety system. Iffor any reason, either prior to or during a given surgical procedure,the tracking system loses its target, the laser is disabled from firing.Various options are available for blocking emission from the apparatusonce the tracking assembly has verified the loss of a tracking signal.

[0027] No previous surgical laser system has employed the efficaciouscombination of features as disclosed herein. For example, in previousart, Bille et al. (U.S. Pat. No. 4,848,340) and Crane (U.S. Pat. No.4,443,075) taught tracking techniques to follow tissue movements whichmight occur during surgery, but did not teach simultaneous 3D imagingwithin the tissue to monitor the effects of surgery on the tissue andprovide requisite safety margins; L'Esperance (U.S. Pat. No. 4,669,466and 4,665,913) also did not suggest any aspects of 3D imaging, teachingonly laser surgery on the anterior surface of the cornea; Bille (U.S.Pat. No. 4,579,430) shows a retina scanner, but does not teachsimultaneous tracking. Bille et al. (U.S. Pat. No. 4,881,808) teach animaging system and incorporate a tracker and a beam guidance system byreference (per U.S. Pat. Nos. 4,848,340 and 4,901,718, respectively) butfail to address the very difficult challenges involved in achieving asmooth combination of all these aspects into a single surgical laserunit with built-in high reliability features. By contrast, it is theunique integration of several such diverse aspects (including mapping,imaging, tracking, precision laser cutting and user interface),precisely yet inexpensively, into a fully automated workstation, theuses of which are transparent to the user, that is the main subject ofthe present invention. The methods and apparatus disclosed herein arethus expected to enhance the capabilities of a surgeon/user inaccomplishing increasingly more precise surgical interventions in afaster and more predictable manner. Enhanced safety is expected to be anatural outcome of the methods and apparatus taught herein in that thesurgery will be performed without many of the risks associated withcompeting methods and apparatus as described by L'Esperance (U.S. Pat.Nos. 4,669,466 and 4,665,913), Srinivasian (U.S. Pat. No. 4,784,135),Bille et al. (U.S. Pat. Nos. 4,848,340; 4,881,808; and 4,907,586),Frankhauser (U.S. Pat. No. 4,391,275), Aron-Rosa (U.S. Pat. No.4,309,998), Crane (U.S. Pat. No. 4,443,075), and others.

SUMMARY OF THE INVENTION

[0028] An embodiment of the present invention is herein disclosed,comprising a method, apparatus, and system for precision laser basedmicrosurgery or other laser-based micromachining, and including thefollowing elements, each of which is described below.

[0029] A final objective (lens), the axial position of which relative tothe tear layer of the corneal vertex (or to a more general target), isheld constant by an axial tracking means, and through which pass alloptical radiations emitted or accepted by the system. (2) An axialtracking means (including associated optics) for maintaining constantseparation between the final objective and its target (which is to bedistinguished from the (common) target for the treatment means and theparallax ranging means, and also from the target for the viewing means)as that target moves axially along the final objective's centerline. Theaxial tracking means includes a compensation means to preclude it frombeing adversely affected by the transverse tracking means. (3) Atransverse tracking means (including optics) for maintaining constantaiming between the treatment and parallax ranging means and their(common) target, and between the viewing means and its target, as thosetargets move (together) transversely to the final objective'scenterline. (4) A treatment means for effecting the actual lasermicrosurgery/micromachining, including a laser, laser-beam directingoptics, a treatment aiming means (with optics), and a treatment focusingmeans (also including optics), all of which are actuated by acomputerized control means. (5) A parallax ranging means, which sharesoptics for the treatment aiming and focusing means, for positioning thecommon focus of the treatment parallax ranging means at a desiredlocation (independent of the target identified above) by use of theviewing means and without requiring the actual operation to beperformed. (6) A viewing means, comprising optics and a low-light-levelTV camera, for presenting to the surgeon/user, on the display means, anadjustably magnified image of the volume adjacent to the viewing target,which target may be chosen by the user independently of the othertargets identified above. (7) A computerized control means, including auser interface presented on the display means, which performscalculations and accepts and issues signals in order to execute thevarious functions of the overall system. (8) A display means forpresenting to the surgeon/user the image from the viewing means pluscomputer-generated overlays from the user interface: such overlaysinclude not only menus but also textual and graphic representations ofaspects such as the topography of the cornea (or more general surfacesassociated with the various targets) and the microsurgery/micromachiningtemplates to be used. (9) A profiling means, including optics, one ormore (patterned) profilometry illuminators, and a TV camera, to generatethe data from which the computerized control means can calculate thetopography of the cornea (or, in other embodiments, a more generalsurface). (10) An output measurement means to measure parameters of thelaser radiation delivered to the eye of the patient or the workpiece.(11) Various illumination means, such as the profilometry illuminators,the coaxial illuminator, and the slit illuminator, to provide the lightsource(s) for the profilometry means, the transverse tracking means andthe viewing means.

[0030] The present invention is expected to be useful in a variety ofmedical specialties, especially wherever the positioning accuracy oflaser lesions is critical and where accurate containment of the spatialextent of a laser lesion is desirable. Much of the following discussionswill be directed at ophthalmic applications and specifically cornealrefractive surgery. This should not be viewed as a limitation on theapplicability of the apparatus and method of the present invention.Alternate embodiments of the invention are expected to play a role inseveral other medical applications.

[0031] The system is also useful for non-medical operations, such asindustrial operations, especially micromachining and short repair ofmicrochips, wherein a focused laser beam is used to perform highprecision operations on an object subject to movement, or in theautomated inspection and correction of errors in the manufacture ofmicroprocessors and high-density integrated circuits.

[0032] In specific applications to corneal procedures, the presentinvention is intended to provide a means by which an ophthalmologist can(a) observe the patient's eye at both low magnification to orient theprocedure and at progressively higher magnification to provide greatresolution for finer and more accurate procedures, (b) access on-linediagnostic information as to the shape of one or more relevant surfacesor of tissue layers to be treated, (c) describe a pattern of shots toeffect a particular lesion shape without requiring manual aiming of eachshot by the surgeon, (d) provide a therapeutic laser beam propagatingthrough a beam steering and focusing delivery system which can localizethe laser lesions at a particular depth in the immediate neighborhood ofthe laser focal point without appreciable damage elsewhere and withminimal peripheral necrosis or thermal damage surrounding the affectedvolume, and (e) provide a target tracking system that can minimize theerror in positioning the pattern of the laser lesion in a moving target.

[0033] In the user interface, a video monitor screen is provided infront of the surgeon, and the screen provides a variety of choices forimaging and diagnostic information. Among the selections available tothe ophthalmologist, for example, is a live video image of the eyesuperimposed over sectional perspectives of the shape of the cornealanterior surface and displayed along with the location where theproposed surgical lesion is situated. Another choice is to display awire-mesh contour elevation map of said corneal surface together with animbedded display of the proposed lesion. These selections can all beenlarged by using the zoom option which augments the live video image,and proportionally also the wire-mesh surface contour, the perspectiveviews of the surface, and all other relevant diagnostics.

[0034] Additionally, a library of patterns is available so that thecomputer can generate templates based on the optical correctionprescribed (generated off-line by the physician's “refraction” of thepatient) and the measured topography (which templates will automaticallycorrect for edge effects, based on built-in expert-system computationalcapability). The surgeon/user can move the templates on the screen bymeans of a trackball, mouse, or other standard pointing device formanipulating points on a video screen and thus, define the shape of thedesired lesion and situate it at the optimal treatment location. Thesetemplates serve the additional function, once finally approved by thesurgeon/user, of automatically controlling the path of the firing of thelaser as well as the size and location of the laser-generated lesions tobe formed in the course of the microsurgery. Since particular templatescan be stored in computer memory, the surgeon/user may, as experiencewith the apparatus develops, draw on a bank of prior knowledge relatingto a particular form of microsurgery, such as ophthalmic surgerydirected to a specific type of correction. A physician may thereforechoose to select from a set of pre-existing templates containing hispreferred prescriptions, lay the template, in effect, on thecomputer-generated image of the region, and resize and/or re-scale thetemplate to match the particular patient/eye characteristics. Thesurgery can then be executed automatically in a precisely controlledmanner, based on the computer programming sense.

[0035] Such a pre-existing library of templates is also useful in theexecution of controlled animal studies. It should be noted, however,that without the accompanying three-dimensional targeting capability andthe automatic image stabilization means contained within the hardware ofthe present invention, the utility of template-generated surgery alonewould be severely limited either to no-sensitive tissues (where highthree dimensional precision is not usually a consideration) or torelatively stationary or immobilized targets (not usually available athigh magnification in a biological system which is “alive).

[0036] In another embodiment of the methods and hardware of the presentinvention, templates can also be generated and stored in similar mannerfor procedures other than corneal refractive surgery, includingiridotomy, posterior capsulotomy, trabeculoplasty, keratotomy, and thelike.

[0037] Among the advantages of the present invention is the modulardesign of the multiple assemblies. The multiple assemblies are eachindividually supported on kinematic mounts. These mounts allow for theseparate construction of the multiple assemblies, their alignment totooling jigs individually, and the precise “hard-aligning” of themultiple assemblies into a complex optical system. Although suchkinematic mounts can add, somewhat, to manufacturing costs, they saveconsiderable alignment time during the assembly of the apparatus andprovide a greater measure of reliability that the apparatus shall remainin operational alignment during continued use by non-technicalsurgeon/users.

[0038] Using the instruments of the present invention, the surgeon cangenerate a proposed pattern of therapeutic treatment, can compare thepattern to the actual tissues targeted, can compare his proposed surgerywith what other surgeons have done in similar situations, and can stillhave the assurance that when he is finally satisfied with the proposedprocedure, he can push a button to cause the desired surgery to becarried out at a high rate of independently targeted shots per second.This speed minimizes the risk during surgery at catastrophic patientmotion.

[0039] In addition, the surgeon has at his disposal a fast reliablesafety means, whereby the laser firing is interrupted automatically,should any conditions arise to warrant such interruption of theprocedure. The surgeon can also temporarily disable the laser fromfiring at an point during the course of the surgery via suitable manualcontrols.

[0040] The tracking subsystem of the invention serves two importantpurposes: it tracks and follows the movements of the patient'stissue—not only the voluntary movements which can be damped withspecialize treatment, but also the involuntary movements which are moredifficult to control on a living specimen—and continuously re-presentsan image of the same section of tissue. Thus, the surgeon/user isprovided a continuous, substantially immobilized view of that tissueregardless of patient movements; and it further provides a fail-safemeans for immediately stopping the action of the surgical laser beam inthe even the tracking is lost, i.e., the tissue is not recognized by thetracking algorithm following the motion, per the discussion on safetyfeatures above.

[0041] In accordance with the invention, fast imaging and tracking areachieved using the combined effects of a pivoting tracking mirror whichmay be under the directional control of a piezoelectric orelectromagnetic transducer, or other rapid servo device to pursue eyemotions in a plane perpendicular to the optical axis of the finalfocusing lens (also referred to herein as the X-Y plane), coupled with amotor drive which translates the otherwise fixed final focusing lensassembly along the axial direction of the final focusing lens, hereindenoted as the Z axis. Thus, three dimensional motions which fall withinthe domain of capture of the tracking system can be observed, pursuedand captured.

[0042] Fast response times are possible with the described embodiment ofthe invention, limited by the ultimate speed of the tracking detector,the computational capabilities of the apparatus microprocessors and datatransfer rates, and the moment of inertia of the tracking servo mirror.It has been determined that such closed-loop target recognition andtracking should occur at least at a rate of approximately 20-to-40 Hz inorder to compensate for involuntary eye motion and thus, provide asignificant improvement over human reaction times. Tracking rates on theorder of 100 Hz for full amplitudes on the order of >1 mm (about 5°) inthe transverse direction and in excess of 40 Hz over a range of +2 mmaxially, would ultimately be achievable with some improvements based onthe methods and system of the present system.

[0043] In a preferred embodiment of the present invention, the trackingsensors, or detectors, in combination with their circuitry, should becapable of high spatial resolution. Examples are linear position sensingdetectors and quadrant detectors. For corneal refractive surgery, thelimbus of the eye provides a landmark ideally suited for such detectors.In the retina, landmarks such as the optic disk, or vesselconfigurations can similarly provide landmarks upon which a magnifiedview can serve as the tracking landmark. In the present invention, anynatural eye feature located in proximity of and structurally contiguousto the target site will serve as the tracking landmark. The importantobservation is that the location of the tracking landmark must respondto forces and pressures in a manner similar to the targeted tissues, yetit cannot be coincident with the precise target site itself, since thissite will change during the course of the surgery.

[0044] Since the limbus is the outer edge of the cornea, it is expectedthat the limbus will respond to changes in position in a similar mannerto other corneal tissues. The limbus further has the advantage of beingcontiguous to the sclera. Correspondingly, it is expected that thetransient displacements occasioned by the impact of the laser pulse onthe target site will be damped sufficiently at the limbus so as to notinduce fictitious tracking signals. Such fictitious tracking signalswould normally be a frequent observation if the present invention wereto use, for example, a mark on the surface of the cornea in the vicinityof the operative site or a remote symmetry axis. Similar considerationsapply when selecting a tracking landmark in other eye segments.

[0045] By incorporating intensified cameras, the present instrument andsystem is of high sensitivity, requiring only low levels ofillumination, and produces video images of high contrast and highresolution. Illumination levels are kept well within established safetylevels for the human eye. With the optics of the present system thepatient's tissue is observed from an appreciable distance, sufficientfor comfort to the patient even during surgery, and sufficient to permitthe surgeon/user ready access to the patient in case of emergency, toinsure safety at all times, to reassure the patient, or for any otherreason which the surgeon/user may feel justifiable.

[0046] Zoom optics are included so that the physician an select a rangeof magnification for the video image, which maybe from about, say 15× to200×. Different zooming ranges may be appropriate for different types ofsurgical procedures while maintaining an overall zooming capability ofapproximately 15-fold. The viewing system may be refocused in depth aswell as transversely, independent of the treatment beam, as desired.

[0047] In one embodiment of the present invention, a system for use inophthalmic laser surgery includes a laser source with sufficient outputpower to effect a desired type of surgery in the ocular tissue, alongwith an optical path means for delivering the laser beam, including beamdirecting and focusing means for controlling the aim and depth of focusof the laser beam. In a preferred embodiment of the present invention, alaser firing up to 250 shots per second is employed. Such a laser devicecan generate an intricate pattern consisting of 50,000 shots aimedseparately at different locations in under 4 minutes. For most types ofophthalmic surgery procedures falling in the domain of application forthe system disclosed herein, the method of deposition of the laser pulseenergy onto the target site calls for achieving irradiances at thetarget site above the threshold for ionization of molecules within thetarget site and giving rise to an avalanche process culminating inplasma formation. Since the maximal diameter of the lesion willconsequently not be determined by the theoretical spot size of the laserbeam but by the maximal outward expansion of the cavitation inducedduring plasma collapse, and since the maximal lesion capacity of theplasma is related to the amount of energy transferred into the plasmavolume (and subsequently into a shock wave) by the laser pulse,considerable attention is needed to maintain the laser pulse energywithin narrow variation tolerances. In one preferred embodiment of thepresent invention, this is achieved by a closed feedback loop, whereineach laser pulse emitted by the system is sampled to determine theactual energy being emitted. Any trends in emission energy can thus beidentified allowing subsequent emitted pulse energies to be adjustedaccordingly.

[0048] U.S. Food and Drug Agency regulations for medical laser devicescurrently require manufacturers of said devices to provide a means formeasuring the output delivered to the human body to within an accuracyof +/−20%. There is no specification on emission tolerances for thelaser beyond the constraints of safety and efficacy. However,verification of average pulse emission does not preclude 50% variationsbetween consecutive pulses in a firing sequence. Such variation range isone of the reasons why “misfires” occur in many ophthahnic devices. Itis not that the laser failed to fire, but that insufficient energy wasemitted to achieve the desired or expected result because of unforeseenand undetected energy variations. For an automated system, such as thepresent invention, the emission for the laser needs to be monitored andadjusted to achieve far narrower pulse-to-pulse error tolerances.

[0049] In summary, it is among the objects of the present invention togreatly improve the accuracy, speed, range, reliability, versatility,safety, and efficacy of laser surgery, particularly ophthalmic surgery,by a system and instrument which continuously presents information tothe surgeon/user during surgery as to the precise location, aim, anddepth of the surgical laser and also as to surrounding features of thesubject tissue, in three-dimensions. It is also an object of theinvention to track movements of the subject tissue during surgery,particularly critical in eye surgery where eye movements can be veryrapid and involuntary. It is further an object of the invention toprovide a safe means of first establishing a reproducible firingsequence positioned in a three-dimensional space, and then firing thesequence in high repetition rates, thus obviating the time-consumingneed to repetitively inspect, aim, and fire each shot before proceedingto the next target. Still another object is to provide a systemapplicable to non-medical fields wherein a laser beam is used to effecta precise operation on a target or series of targets subject to movementduring the procedure. These and other objects, advantages, and featuresof the invention will be apparent from the following description ofpreferred embodiments, considered along with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0050]FIG. 1 is a block diagram of an instrument or workstation forperforming precision laser surgery in accordance with the principles ofthe present invention. In FIG. 1 the workstation is configured forophthalmic surgery.

[0051]FIG. 2 is a block diagram of an instrument or workstationindicating the path of the laser energy pulse as it propagates throughthe system along with the functions of control and information flowamong various optical components, detectors, and controllers formonitoring the energy of the laser pulse and maintaining the emissionwithin prescribed narrow error tolerances.

[0052]FIG. 3 is a block diagram of the path for light traveling from andback to the depth ranging or Z-plane tracking means, together with theloop for information flow to the computer control means and back to theposition means.

[0053]FIG. 4 is a block diagram showing the light path from the parallaxranging assembly to the eye and the control path from the imaging videocamera to the video monitoring display means. The light path from theeye back to the imaging camera is also indicated in this Fig.

[0054]FIG. 5 is a block diagram of the workstation in which the lightpaths and control loops for the X-Y place tracking means are shown.

[0055]FIG. 5A shows the image of the iris incident on the two quadrantdetectors used in a preferred embodiment of the sensor for X-Y tracking.

[0056]FIG. 6 is a block diagram indicating the interplay of the imagingmeans with the video monitor display.

[0057]FIG. 7 is another block diagram indicating the light path betweenthe topography assembly and the eye together with the control loop andinterface with the video monitor display. The displays generated by thetopography loop depicted in this Fig. are overlayed the live image shownin FIG. 7 by the computer control assembly.

[0058]FIG. 8 is a scale drawing of one embodiment of the instrument ofthe present invention.

[0059]FIGS. 9a-9 c represent three perspectives of an artistic renditionof an ergonomic configuration of the workstation. The system wasdesigned to accommodate the engineering subassemblies in a maximallycompact manner while providing a large amount of clear space for thepatient.

[0060]FIG. 10 is a detailed block diagram illustrating the functionalinterdependence among the various optical subsystems.

[0061]FIG. 11 is a block diagram showing the sequence of control andinformation flow from the user interface elements to the firing of thelaser.

[0062]FIG. 12 is a photograph of a user interface screen showing aselection of computer-generated patterns which can further be modifiedusing “CAD/CAM-like” editing functions, such as are contained in a“utilities” module.

[0063]FIG. 13 is an illustration of a user interface screen showing awindow of a sample “treatment” menu used to select treatment eyesegments, set lesion shapes, choose operating parameters correspondingto the template designated procedure or other functions.

[0064]FIG. 14 is a photograph showing the same sample templates as FIG.12, and highlighting an example of a pull-down “set parameters” menu.

[0065]FIG. 15 is a topographical representation of a three-dimensionaleye surface as seen from the user/interface screen, highlighting asample “diagnostic” module.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

[0066] In the drawings, FIG. 1 shows a block diagram for the fundamentalassemblies of a complete precision laser surgery and/ordiagnostic/analytical instrument 10 in accordance with the principles ofthe present invention, in the form of a workstation. Not shown are thesupport station housing the video monitor means, the power supplies, thefire control/safety switch, and other accessories for the workstation.

[0067] Although the system, apparatus, and method of the invention areillustrated and discussed with reference to ophthalmic surgery anddiagnosis, it should be understood that the invention encompasses othertypes of medical diagnostic and surgical procedures, as well asnon-medical operations (e.g., semiconductor processing, such asprecision wafer fabrication, short repair using lasers and othermicromachining techniques.)

[0068] The instrument and system 10 of the invention include controls 16for a vision system and laser firing, enabling the surgeon/user tosurvey the topography and internal features of the tissue to be operatedupon (the eye in the illustrated workstation) via a video means 19, and,via the computerized control means, to precisely control the timing aswell as the direction, depth and spatial pattern of firing of a laserbeam in three-dimensions. As will be explained below, the surgeon maycontrol the firing of the laser with “templates” which can besuperimposed over an image of the tissue being operated upon, and whichenable an automatic tracing of desired laser firing pattern based uponprior experience or a surgeon's insights with similar surgicalprocedures. The templates may be pre-programmed or generated anew foreach patient, as the case requires.

[0069] The system also includes a final objective lens or focusing lensor front lens 17 (an element of the microscope assembly, as explainedbelow), through which images are taken and through which the laser beamis directed at the subject tissue. In a preferred embodiment of thesystem, an axial illuminating light beam may be projected at the tissuethrough the topography assembly 98 and the final objective lens 17. Inother embodiments of the present invention, an off-axis slitilluminator, providing a ribbon-shaped illuminating light beam, may beused to augment and/or replace the axial illumination technique, (SeeHowland et al. “Noninvasive Assessment of the Visual System TopicalMeeting,” Santa Fe, Feb. 4-7, 1991) depending on the particular kind ofsurgical procedure or error tolerances required thereof. Th instrument10 may contain, in addition, the therapeutic laser 87, the surgicalmicroscope 86, an X-Y tracking assembly 85, a depth ranging microscope84, a parallax depth ranging assembly 82, various illuminators, and thebeam steering and focusing assembly 81. All of these assemblies share anoptical path defined by the final tracking mirror 72 and the lens 17.

[0070] Tracking mirror 72 represents a key element in the system, inthat it is in the path of light (whether transmitted or reflected),generated and/or acquired by all the various subassemblies of theworkstation, excepting only the slit illuminator (of the alternateembodiment, not shown in FIG. 1). In alternate embodiments of theinvention, the tracking mirror may be driven either piezoelectrically orelectromagnetically. A piezoelectric driver uses the change in shape ofa quartz crystal in response to an electric current to move the mirror.An electromagnetic driver uses a coil of wire in a magnetic field whichis made to move by passing an electric current through the coil. Theelectromagnetic driver is similar in function to a voice coil of anaudio speaker. In either embodiment, the speed (or, more accurately, theacceleration) of the entire tracking system is limited by the responseof the drivers and the mirror's moment of inertia.

[0071] Most of the major components and subassemblies, shown in theblock diagram of FIG. 1, are disclosed separately and have beenincorporated herein by reference. However, the combination of theseseparate inventions into system 10, the methods by which they can bemade to work in concert as an integrated unit, and the enhancedcapabilities this entails in a surgical environment are the subject ofthe present invention.

[0072] For example, the topography technique requires establishingprecisely the distance from the surface to be measured to theappropriate principal lane of the front focusing lens. Whereas there areseveral methods for establishing said distance, the modified confocaltechnique described by Fountain (U.S. Pat. No. 5,283,598) represents apreferred embodiment of such a measuring technique, incorporated byreference into the present invention. Since in surgery the targets arelive tissue and are continuously in motion, to achieve high levels ofaccuracy requires that the surface to be measured by way of thetopography assembly also remain stable with respect to the measuringsensors located within topography assembly 98, zoom video assembly 86,and the known focal point of laser 87. This is achieved by continuouslyadjusting the position of final focusing lens 17 along the axialdirection as further described by Fountain in the '598 patent.

[0073]FIG. 2 shows the light path 71 as it emerges from laser 87, passesthrough the external energy regulator 83, is expanded and directed inthe beam steering and focusing assembly 81 as further described byFountain et al. in U.S. Pat. No. 5,391,165 and is aimed via trackingmirror 72 and through front focusing lens 17 onto the prescribed targetsite. In a preferred embodiment of the invention, tracking mirror 72will have an optical coating which will permit a small portion of thelaser energy to continue through tracking mirror 72, along path 73 to bedetected in energy monitoring assembly 80, as depicted in FIG. 2.

[0074] The pulse energy sensed in energy monitoring assembly 80 iselectronically relayed to the computer control assembly 16 which in turnanalyzes the output energy from laser 87 and adjusts the proportion oflaser energy of subsequent laser pulses to pass through energy regulator83. In an embodiment of the present invention, energy regulator 83 is apolarizer adjusted to be “crossed” with the polarized laser pulse,preceded by a rotatable half-wave retardation plate. Energy monitor 80consists of an integrating sphere and detector which can record energyon a pulse-by-pulse basis. The energy detector calculates weightedexponential moving averages, modified with a weighting factor, as wellas the rate of change of the running average. The accuracy ofmeasurement of the pulse energy is within 5%, based on calibrationagainst standard energy meters (e.g., Molectron, Scientech).

[0075] In a preferred embodiment of system 10, the steering, focusing,and aiming subassembly 81 may consist of a beam expander 22 thatprovides depth of focus variations through change of collimation, and adual set of Risley prisms (also known as Herschel prisms) 21 to steerand aim the beam, as described in detail in the '165 patent by Fountainet al. (previously made of record).

[0076] Beam expander 22 may comprise a set of lenses 23, a stepper motor41, and a slide 43 with 75 mm traverse corresponding to ˜25 mm in theeye. Beam focus accuracy to within 10 μm can be provided in this manner,based on standard optical components. The Risley prisms are selected aspreferred means of beam steering and directing because of lower momentof inertia and shorter lever arm as compared to alternatives, such asgimbaled mirrors. The lower moment of inertia inherently allows fasteraiming (which is enhanced by the use of cylindrical coordinates, thesebeing more natural for the eye than Cartesian coordinates), while theshorter lever arm permits aiming further off-axis without beam-clipping(vignetting) at the aperture of objective lens 17.

[0077] In a preferred embodiment of the invention, surgical laser 17emits radiation in the visible wavelength range to take advantage of thetransmission properties of visible light in the optically clear tissuesof the human eye. One preferred embodiment of the invention uses afrequency doubled Nd:YAG laser, producing sufficiently short durationpulses (shorter than a few hundred nanoseconds, and preferably shorterthan 10 nanoseconds) to limit the amount of energy required to ionizematerial as discussed further below.

[0078] In alternative embodiments, laser 87 may be one of several typesof flashlamp- or diode-pumped solid-state lasers (such as, Nd:YAG,Nd:YLF, HoYLF, Er:YAG, alexandrite, Ti:sapphire or others) operating inthe fundamental or a frequency-multiplied mode, a semiconductor laser,or an argon, excimer, nitrogen, dye, or any of a host of differentlaser, or combinations thereof, currently available or in development.The present invention can be used with any of a wide variety of lasersby specifying different coatings where necessary for the opticalsurfaces. A quartz and magnesium fluoride focusing element is availableas the element 17 to accommodate ultraviolet lasers whether they beexcimer lasers or frequency shifted solid-state lasers. One of thefeatures of the present invention is that is it is not laser specific,but represents a surgical instrument intended to enhance the efficacy ofany therapeutic laser. Laser 87 preferably produces a pulsed beam whichis controllable as to the level of energy per pulse, pulse peak power,and repetition rate. For ophthalmic applications which do not seek togenerate laser lesions below the front surface of the cornea, orwherever incising the eye is an acceptable option as a preliminary or aspart of the procedure, then excimer lasers, holmium lasers, carbondioxide lasers, or some other ultraviolet or infrared laser may be anacceptable modality. In one embodiment of the present invention, thesurgeon is not restricted to surface effects or to incising the eye.With the same visible wavelength laser (for example, a frequency doubledNd:YAG) the surgeon can select any tissue depth (whether on the cornealsurface or below, whether on the posterior lens capsule or in the lensnucleus) at which to generate an effect without the necessity ofexchanging laser modalities for different eye segments, provided thereremains an optically clear path to the targeted layer in thecorresponding visible range.

[0079] In the event of a non-visible-wavelength laser beam is used(e.g., strictly for ablating the front surface of the cornea, orstrictly for coagulating blood vessels in the retina, or strictly forphotodisrupting membranes on the posterior capsule) some variations inthe optical configuration of system 10 will likely be required.

[0080]FIG. 3 shows the information path for depth ranger assembly 84that measures the distance from front focusing lens 17 to the surface ofthe eye 69 and continuously adjusts the position of front focusing lens17 along path 88. In a preferred embodiment of the present invention,the path length 88 over which front focusing lens 17 is adjusted is 5mm. The system comprising subassembly 84 together with lens 17 and theintervening optics, is sometimes referred to herein as the confocalmicroscope. It uses optical elements in common with other equipment ofsystem 10, namely the tracking servo mirror 72 and beam splitters 65,66. Focusing lens 17 is adjusted as to focus, along a Z-axis, inresponse to shifts in the depth of the subject tissue feature, so thatthe system always returns to a focus on the corneal vertex 56 (the partof the cornea that is closest to the objective lens).

[0081] Included in the depth ranger assembly 84 are depth tracking or“Z-axis” tracking sensors 50 which detect a change in location of thesurface 69 as described by Fountain (in a U.S. Pat. No. 5,283,598,previously incorporated) and relay the information to the computercontrol assembly 16 which computes a new desired position for frontobjective lens assembly 17 and issues instruction to a motor drive torelocate said lens assembly 17 to the desired new location. Aclosed-loop is thus described which incorporates the live movements ofeye surface 69 within the decision process of adjusting the focal pointof lens assembly 17, to within given tolerances. In this embodiment, thecapture range for axial acquisition is within +/−0.2 mm and trackingrates in excess of 40 Hz are within the servo loop capability formaximum ranges on the order of 2 mm.

[0082] Since mirrors and beam 64, 68, and 72, together with beamsplitting cubes 65, 66 and 67, link the other assemblies of system 10into a common axial path passing through lens focusing assembly 17, theycan all be referred to the lens assembly 17 as if the distance betweenlens 17 and eye surface 69 were to remain constant. This is a majorsimplification in the manner in which eye surgery can be performed inthat the surgeon need no longer be continuously monitoring eye movementto verify a constantly changing focal position within the patient's eye.

[0083] For procedures where the targeted tissue layers lie posterior tothe cornea, the surgeon/user will have the use of the parallax depthranging instrument 88, as shown in FIG. 4. This assembly relies on theintersection of two beams of light (from, e.g., a He—Ne illuminatorlaser) converging to a common point on a given surface. In oneembodiment, the parallax ranger allows mapping of a mesh of points,acquired through judicious adjustment of the zoom camera to shortdepth-of-focus (maximum magnification), which, along with correspondingvariation of the focus on the parallax ranger, produces a series ofdiffraction limited spots on the structures behind the cornea (iris,lens, etc.). In this manner, the resulting surface will define a desiredtemplate.

[0084] The inclusion of a parallax ranger within instrument 10 overcomesdifficulties commonly associated with specular reflection techniquesused for detection of the location and measurement of ocular features.Basically, only the tear surface layer overlying the corneal surfaceepithelium is usually detectable and measurable by specular lightreflection techniques. The reflected light signal is generallyinsufficient for the extraction of topographic information of theendothelium surface of the cornea (<0.02% reflection versus 4% from theepithelium), let alone for characterization of the three-dimensionalshape of the anterior and posterior capsules of the crystalline lens ofthe human eye. The parallax ranger unit provides the surgeon/user withthe option of using a combination of standard techniques which rely onimages of a target site. Thus, the surgeon/user can identify, to withinthe inherent error tolerances of the technique, when the instrument isfocused on a given surface. The precise focal point of the beam can thenbe varied by altering the incoming beam divergence by way of defocusinga beam expander means 22 (included within assembly 81). By redefiningthe origin of a given procedure to coincide with the depth at which theparallax ranger is focused on a surface, this new identified surfacebecomes the reference surface for performing a surgical procedure. Viathe user interface (See Sklar et al., U.S. Pat. No. 5,098,426 and U.S.patent application Ser. No. 475,657 (now abandoned), previouslyincorporated by reference), the surgeon/user can then define lesiontemplates or configurations to be performed at a given depth withrespect to the new identified surface.

[0085] Similarly, the motion of the eye along a plane perpendicular tothe Z-axis of front focusing lens assembly 17 also needs to bestabilized. This is achieved using the X-Y tracking path shown in FIG.5. Intrinsic to any tracking scheme is the choice of what is to betracked. If the eye were a non-deformable body, then any landmark on orin the eye would suffice for defining the motion of said material.However, the eye neither moves nor deforms as a rigid body.Consequently, in order to define the location of a moving tissue layerwithin the eye, the tracking landmark must be located contiguous to thetargeted tissue and should mechanically respond in a manner similar tothe targeted issue.

[0086] For corneal refractive surgery, the eye limbus at the radiallyoutward edge of the cornea satisfies these constraints. It has theadvantage of not only moving with the cornea—inasmuch as it is a part ofthe cornea—but, since it likewise is connected to the sclera, it willnot respond as dramatically to the transient deformations associatedwith the microsurgery. In effect, pursuing the motions of the limbuswill allow the computerized control system to replicate the templatepattern presented on the display by the user interface, even though theeye surface will be appreciably deforming during the course of thesurgical procedure.

[0087] In one embodiment of the invention, the transverse X-Y trackingdetector consists of high speed quadrant detectors and a microprocessorsuch that updated position information is fed to the tracking mirror atfrequencies substantially higher than the repetition rate of the laser,or the frame rate of the imaging camera. The response time of thetracking detector and processor should be sufficiently faster than themaximum repetition rate of the laser, so that laser firing can bedisabled, if necessary. The response time of the detector and processorshould also be higher than that of the driven tracking mirror, whichmust be capable of sufficiently high acceleration and velocity tocompensate for the fastest motion possible by the intended target.

[0088] In FIG. 5, light from limbus 70 passes through the objective lensassembly 17, is reflected by the X-Y tracking mirror assembly 72, and ispropagated via beam splitting cubes 65, 66 through viewing lens 63 to bereflected off beam splitter 67 to sensors of X-Y tracking assembly 85.In one preferred embodiment of the present invention, a spatiallysensitive sensor 50 comprising two quadrant detectors is used to trackan image of the outer rim (at the limbus) of the iris 32. As shown inFIG. 5A, the image of quadrant detectors (each with four quadrants 35,in this example) will then consist of a bright lune-shaped fieldcorresponding to sclera 33, adjacent to a darker field representing animage of the iris 32. The very dark central core which is an image ofpupil 34, is not captured by the detectors, as FIG. 5A illustrates,leaving a single sharp boundary to track. With various cells of thequadrant detector connected through differential amplifiers andnormalized by the sum, the resultant signals are sensitive only to theposition of the centroid of illumination of any of the above patterns.Quadrant detectors integrate the image illumination striking eachquarter of the detector face. The luminosity impingent on the detectorfaces will then generate voltage differences corresponding to theintegrated differences in light hitting the detector parts. A change inbackground light intensity will be ignored, as the increase across thefour (or eight) quadrants 35 of the detector face will remain the same.Voltage sums and differences among the quadrants serve to establish therelative direction of motion between two contiguous readings of thelimbus position. A shift in intensity at the sensor is thereby traced tomotion of the limbus. These dedicated quadrant detectors record voltagechanges extremely rapidly and can observe and quantify contrast changesand edge motions in less than 100 ms. In alternate embodiments,similarly fast but more sensitive position sensing detectors are used inthis application, yielding enhanced performance at even lower lightlevels.

[0089] The voltage change information is relayed to the computer controlassembly 16 wherein the actual coordinate shift is calculated. Controlassembly 16 then determines the angular corrections to be relayed to theX-Y tracking mirror assembly 72 and activates a voice coil or otherelectromagnetic drive assembly to pivot the orientation of mirror 72 soas to stabilize the X-Y motion of limbus 70 with respect to system 10.This embodiment of a tracking system uses entirely analog signals andtechniques to achieve tracking and can be made to work significantlymore rapidly than even the fastest involuntary motions of the eye.

[0090] In one preferred embodiment of the invention, the range of use,or travel, is 2 mm in the X-Y plane. For ophthalmic applications, wherethe principal motions of the eye are rotations, it is often preferableto define the range of use in terms of angular sweep of the eye. Forexample, an angular motion of the eye of 5° falls well within the domainof use of the X-Y tracking system. For a sighted human patient, it hasbeen estimated that such range of use will acquire an eye looking at animage point located in the far field (relative to the patient) andsituated along the optical axis of the apparatus.

[0091] The transducers of the tracking system adjust the position of theX-Y mirror along two rotational axes at accelerations on the target inexcess of 20 μm/ms for full amplitudes of over 2 mm, based onmicroprocessor-provided information relating to the new location of thesame tissue. 1931 Eye surface 69 may be displaced in translation and/orby rotational motions centered on the globe of the eye; because the X-Ytracking mirror 72 rotates about a point within its assembly that isdifferent from the eye's center of rotation, a desired change in X-Ytracking mirror position also requires a correction of the X-Y axisposition of the depth ranging and tracking assembly 84. Consequently,the algorithm which pivots the X-Y tracking mirror 72 along paths 61 and62, also must relay instructions to the computerized control system toadjust the depth tracking and ranging assembly 84 so as to maintain thecorrect orientation. The preferred methods to achieve this correctionuse a compensating mirror 60 within the Z-tracking assembly (not shownin FIG. 5).

[0092] The tracking system has the advantage of being able to find anabsolute position of the target even after a temporary loss of tracking.For example, if a surgical procedure is in process and an obstacle, suchas a blinking eyelid in many ophthalmic procedures, interposes thetracking image such that the procedure is interrupted or temporarilyaborted, the tracking system will automatically store in memory the lastposition in the firing sequence so that once the target is againreacquired, the exact location of the next point in the firing sequencecan be determined automatically and the servo mirror be repositionedaccordingly.

[0093]FIG. 6 shows the surgical microscope loop. This subassemblyincludes the low-level-light camera and the zoom optics. The camerapreferably comprises an intensified video camera, for example a siliconintensified target (SIT) tube camera. Alternatively, it can be aconventional video camera in combination with a microchannel-plateintensifier. In either event the camera's sensitivity preferably isabout 1000 times that of a normal video camera, enabling the system tolook at weakly scattered light and targets poorly illuminated for thedesired levels of high magnification at large working distances.

[0094] In a preferred embodiment of the present invention, the systemuses a combination of specular and scattered light techniques fordetecting and identifying diffusely reflecting surfaces, specularlyreflecting surfaces, surface displacements, features, and shapes of thepatient's tissue. This is particularly useful in the eye where it canprove difficult to differentiate between the amorphous tear layeranterior to the cornea and the structured cornea or of the anterior lenscapsule will scatter light. The intensified surgical microscope canproduce an image of these actual cells by forming an image composed bydetecting scattered light. The surgical microscope, as well as thetracking camera, can substantially exclude specularly reflected light bycross polarization of selectively polarized illuminators. Other methodsfor reducing specular reflections preferentially to scattered images arealso possible.

[0095] The microscope optics are designed to provide flat field,anastigmatic, achromatic, nearly diffraction limited imaging withoptical magnification zoomable approximately over a 15-fold range of,say 15×-200×. The magnification is adjustable and is typically selectedto correspond to the largest magnification which can still becomfortably used for situating a lesion (that is, the smallest field ofview which can be used when magnified across the fixed display size ofthe video monitor.) For example, for corneal refractive surgery, wherethe surgeon needs to observe the cornea from limbus to limbus, thiscorresponds to a field of view of approximately 12 to 14 mm. At thescreen, the zoom optics allow for adjustable magnification in the rangeof about 15×-200×, for example. This enables the surgeon to view a verynarrow field, on the order of a millimeter in width, or a much widerfield at lesser magnification. This is useful in enabling the surgeon toassure himself that he is aimed and focused at a particular desiredregion. Zooming can be effective through use of a joystick, trackball,mouse, or other pointing device 42 to access a scroll bar in the userinterface.

[0096] The function of the viewing mirror 68 shown in FIG. 6 is to movethe surgical microscope image on the screen to the left or right or upor down, independent of the aiming of any other subsystem.

[0097]FIG. 7 shows the light path for the topography assembly 98, whichprovides a three-dimensional mapping system directed at the surface ofthe target, e.g., the eye of the patient. In a preferred embodiment ofthe system 10 (as described by Sklar in U.S. Pat. No. 5,054,907 andfurther extended by McMillan and Sklar in U.S. Pat. No. 5,170,193, allof which are incorporated herein by reference), the subassembly 98 maycomprise a light projector 95 including an internal profilometry source90, an illumination mask 96, an optical collection system 94 and aprofilometry assembly consisting of, e.g., an adjustable aperture 99 anda CCD camera 97 equipped with a frame grabber, such as an array of dotsarranged into rings and radial spokes converging to a common center,onto the tear layer of the eye. The reflected images of thepredetermined pattern are collected by the optical assembly 94, whichmay include a set of plates to correct for any astigmatism induce by thetracking mirror 72 and any other interior mirrors, fed into theprofilometer camera 97 through the aperture 99 for analysis. Bycontrolling the angle of acceptance of the light bundle from eachvirtual image, the adjustable aperture acts as a spatial filter,providing a physical representation of the source of paraxial raysthrough trade-offs between resolution and brightness. The cameraincludes mans to digitize and electronically enhance the images. Thesignals are fed to a microprocessor which performs preliminarydisplacement analysis using software means (embedded within controller16) based on mathematical morphological transformations as described bythe '193 patent. The transformations comprise a solution of a set ofcoupled differential equations, whereby the local normals and curvatureparameters are computed at each data point so that the surface can becomputed to within the measurement accuracy, and subsequently displayedon the video screen 20. The methods of light projection and profilometrypermit the system 10 to operate with low intensity light signals toenhance safety and patient comfort while extracting significant signallevels form the noise background.

[0098] In other embodiments of the profilometry assembly, alternativeprojection techniques may be utilized in place of or in addition to themapping and projection means described above. In one embodiment, anexternal profilometry source 89, consisting of an array of LEDs projectsa patter of dots onto the eye in a manner described by McMillan et al.in U.S. Pat. No. 5,283,598. In this embodiment, curvature measurementsof the anterior surface of the cornea can be obtained extending up to 8mm in diameter around the center. Other techniques based on off-axisillumination may utilize, e.g., a slit lamp illuminator 77 to obtainmeasurements of the thickness of the cornea, the depth of the anteriorchamber and/or the thickness of the lens (the latter coupled withstandard keratoscopy methods to correct for corneal curvature). Mountingthe slit lamp at a fixed location relative to a CCD camera (such as 97)and rotating the entire structure around a center axis would alsoprovide a method to collect global corneal data (out to the limbus) yetwithout sacrificing local accuracies, given the simultaneous 3D trackingcapability already contained in the system. In this manner, the domainof topographic measurements can be extended from limbus to limbus whileproviding pachometry data as well. Alternatively, topography methodsbased on Ronchi grating in conjunction with Moire interferometry, oradvanced holographic techniques as discussed by e.g., Varner (inHolographic Nondestructive Testing, Academic Press, New York, 1974 pp.105) and by Bores (in “Proceedings of Ophthalmic Technologies,” SPIE1423, C. A. Puliafito, ed., pp. 28 (1991)) may be utilized in futureembodiments of system 10, if warranted for specific interventions.

[0099]FIG. 8 is a schematic optical layout of a preferred system ofoptics for the instrument of the invention. In FIG. 8, a SchneiderCinelux Ultra 90 mm focal length f/2 lens is combined with a SchneiderTele-Xenar 360 mm focal length f/5.6 lens, matching conjugates to form a4×/0.24 numerical aperture (N.A.) “objective lens” 17 with a workingdistance of 59 mm. This type of design embodies a key feature of thepresent invention, whereby a comfortable distance between the patientand the optics is implemented (sufficient to provide the surgeon/userenough open clear space to easily fit his hands between the front“objective lens” 17 and the patient's eye/target surface 69) whilemaximizing the aperture ratio of the system. A beam splitter between thefront and back lenses of this “objective lens” allows the 90 mm lens toalso serve as the final focusing lens for the laser. A Schneider Xenonf/2 lens, with 28 mm focal length, relays the image to the cameracontained within subassembly 86, with magnifications zoomable from about0.4×-5.4× in this embodiment of the invention. An appropriate field lens58 is used to provide uniform illumination across the image of themaximum 15 mm field of view at the object (eye) and to reduce themagnification. Zooming can be accomplished by computer-and-steppedmotions of both the zoom lens 59 and the camera. The total opticalmagnification is thus zoomable in this embodiment from about 0.8 to 11.With the image incident on a ⅔″ video detector and displayed on a 13″(diagonal) monitor, an additional 19× video magnification is gained,thus a maximum magnification from the target to the screen of about 200×is achieved.

[0100] Another important feature of the optics of the system of theinvention is that the servo tracking mirror 72 actually is positionedinside the “objective lens” assembly (the final element has beendesigned to have sufficient field to accommodate the small misalignmentscaused by the tracking mirror). This enables the system to achieve rapidtracking of ocular features (or other tissue features) in an efficientand relatively simple assembly, without moving an entire objective lensin following the sometimes rapidly moving features.

[0101] The optical system is designed without correction for theaberrations of the eye. For work in the cornea no corrections areneeded. For work at image planes located posteriorly to the cornea, suchas the retina, for example, contact lenses 28 (e.g., Goldman or similar)may be used, as shown in Inset a of FIG. 8.

[0102] As illustrated in FIG. 8, the illuminator light beam containedwithin assembly 82, first is reflected off a turning mirror 73, thentransmitted through mirror 64, to join substantially coaxially with thepath of the laser beam along the beam axis (see FIG. 2). Both beams arethen steered through the beam steering and aiming optics in assembly 81and are reflected off a reflective surface in the polarizing beamsplitter 65 before being incident the tracking mirror 72. The polarizingbeam splitter 65 (along with beam splitter 67) effectively preventinternal back reflections of the laser pulses from the optics of thesystem from damaging or overwhelming the sensitive video microscopecamera contained in assembly 86.

[0103] Also indicated in FIG. 8 are the optical tracking and viewingelements, namely, depth ranging assembly 84, X-Y tracking assembly 85,and surgical microscope 86, all share the same optical path from beamsplitter 66 to the eye. Some key design details of the Z-trackingassembly 84, including the illumination source (such as a red Ne—Nelaser) are shown in Insert b. These are described in more detail in U.S.Pat. No. 5,162,641.

[0104] As FIG. 8 shows, the beam generated by the therapeutic laser 86and parallax ranger 82 are coaxial with each other, but the axis ofthese beams is not necessarily coaxial with the axis of view of theprofilometer camera 97, the topography illumination source 90 or theother tracking/viewing assemblies 84, 85 and 86. This is because ofdirectional steering Risley prism sets 21 embedded within assembly 8.1which are outside the optical path of assemblies 84, 85 and 86, butwithin the optical path of the parallax depth ranger 82 and laser 87.The Risley prisms are steerible via the computerized control assembly 16under the control of the surgeon/user through user interface commands.They provide means for adjusting about the X and Y axis, thus lettingthe physician select different locations for firing the laser, asdisclosed by Fountain & Knopp in U.S. Pat. No. 5,391,165 (which claimspriority from U.S. patent application Ser. No. 07/571,244). Elements 82and 87, therefore, will only be coincident with the axis of view ofdepth tracking assembly 84 when the surgeon aims the laser directly atthe center of the field of view of assembly 84. In other instances theywill share the same “optical path” via elements 72 and 17, but they willnot be on identical axes. The Risley prisms within assembly 81 allowmovement of the actual aim of the therapeutic laser beam from laser 87to a real aiming point which is coincident with the computer-generatedaiming points.

[0105] The set of beam expander lenses 23 preferably are positioned asclose as practical to final objective lens 17, and are initiallyadjusted so as to expand the diameter of the laser pulse emerging fromthe laser cavity and collimate it so that a parallel but expanded beamof light emerges from lens 22. The expanded, collimated beam is incidentupon the final lens 17, and the expanded beam fills the lens to theextent compatible with vignetting for off-axis aiming. Thus, a largediameter beam is focused by lens 17, so that only at the point of focuswithin the eye is the diffraction limited pulsed laser beam effective ingenerating the desired therapeutic lesions in the eye. The depth of thefocal point is varied by adjusting the distance between the two lenses23, which has the effect of changing the degree of collimation and hencethe focus as indicated explicitly in FIG. 8. the surgeon's adjustmentsof the focus of the beam via the computerized control system 16, aresuperimposed on top of the automatic adjustments effected by thetracking system, and net focus changes are carried out by the system.This is easily accomplished using hardware and software associated withthe system which does not in itself form a part of the presentinvention.

[0106] The decoupling of the aiming and viewing functions allowsoff-axis work, which represents a major improvement in the function ofthe system 10, in that off-axis capability is a mandatory feature forcorneal and most other applications. Thus, an independent mirror 68 isinserted upstream of assembly 86 to allow viewing, while aiming isperformed independently in the coaxial illumination path using theRisley prisms 21 of subassembly 81. In an alternative embodiment of thesystem disclosed herein, a secondary angular steering mirror 60 (noexplicitly shown in FIG. 8) may be added in assembly 84, to compensatefor motion imparted by the X-Y tracking mirror which can, for largeenough eye motions, cause the Z-tracking system to “lose lock.”

[0107] Inset c of FIG. 8 shows some schematic detail of the externalslit lamp illuminator, provided in an alternative embodiment of system10 to augment and/or replace the internal profilometry illuminationsource 90, and provide ocular thickness measurements as was describedabove (see discussing following FIG. 7). The slit lamp constitutes theonly element of the system not coaxial with the optical path defined bythe tracking mirror 72 and the “objective lens” 17 common to all theother subassemblies.

[0108]FIGS. 9a, 9 b, and 9 c show three perspectives of an ergonomicrendition of the workstation which incorporates the entire system 10.System 10 in this illustrated embodiment of the invention is intendedfor ophthalmic surgery, with the patient to be seated, as shown in FIG.9a, in a chair 11 with his forehead against a forehead rest 12 and hischin against a chin rest 13, as shown in FIG. 9b. Both forehead and chinrests are fully adjustable. The surgeon/user is free to stand at aconvenient location where he/she can survey the progress of the surgeryas depicted on the video monitor means 18 (containing the video displaymeans 27, including screen 20) as depicted in FIG. 9c, while havingdirect access and observation of the patient, or to sit in a chair 14.The seats 11 and 14 for the patient and the surgeon, respectively,preferably are fully adjustable with e.g., tracks 15 (shown in FIG. 9a)for adjusting proximity to the apparatus and with full height and seatback adjustability.

[0109] A hand held system control switch 24 in FIG. 9a may be providedfor the surgeon/user as a safety device which will both enable the lasertriggering means when sufficient pressure is exerted on device 20 (via asimple toggle switch, for example), or alternatively will immediatelyinterrupt laser firing if pressure on the control means 24 is released.

[0110]FIG. 10 is a functional block diagram showing the principalcomponents and individual control and informational feedback functionsof the precision laser surgery system of the invention, all indicated asbeing under control of a central processing computer 16, designed tointegrate and control the operation of the entire system 10. Thecomputer may include a microprocessor 140, software programs 141, andfirmware 142, as indicated in FIG. 10, as well as a number of othercontrol and indicate features (not indicated) such as the enabling (ordisabling) of internal safety interrupts, a light-emitting diode (LED)display which indicates when the tracking system and target acquisitionsystem are operational and on-target, an LED which lights up when thesystem components have successfully been verified to be performingwithin system specification ranges, an LED indicating power is on, and adedicated video display function to assist in detecting location of asystem malfunction. Note that some key functions in the system arecarried through dedicated microprocessors 150, which, for simplicity,are shown in FIG. 10 sharing the same block as the centralmicroprocessor 140.

[0111] During the start-up phase of system 10, a complete systemverification is performed automatically without further prompting formthe surgeon/user, including a set of internal diagnostics listing thestatus of operational use of the various assemblies. During thisstart-up phase, the assemblies shown in FIG. 10 (and FIG. 1) are eachindividually tested for operational status within prescribed tolerances.If all tolerance levels are satisfied, the user interface screen 20appears and the system is enabled for use. Additional safety LEDsacknowledge sufficient pressure on the laser fire safety interlock inthe hand-held (or, foot pedal) safety device 24, and whether themicroprocessor generated template pattern is in control of the firingsequence.

[0112] As shown in FIG. 10, the central computer (which receivessimultaneous diagnostic measurement and tracking information) closeseach control loop through a central fire control function shown as block100 forming a critical part of the computer control assembly 16. Thisfail-safe mechanism is a key feature provide within the instrument andsystem 10. Thus, the computer, which directly controls laser firing, asindicated by control line 144, automatically interrupts the firingsequence should any of the required operational specifications not bemet (such as loss of tracking, deviation of the pulse energy, etc.). Ifall preset conditions are met, the computer control assembly enables andfires the surgical laser in accordance with preselected templates shown,functionally, as block 6. The required information comprisesconfirmation that the template is still positioned correctly, i.e., thatthe targeted feature of the eye has been tracked within a preselectedtime allotted, so that the images of the eye remain stabilized. If thisconfirmation is not sent (or a contrary signal could be sent signal thattracking is lost), the template controlled laser firing is immediatelyinterrupted, as discussed in more detail below.

[0113] The user interface shown in a block 19 in FIG. 10, communicateswith the central computer unit 16 as indicated by control line 123,though it may also have some controls which do not involve the mainmicroprocessor 140. Thus, if the surgeon wishes to generate a templatefor surgery, as shown in dashed line 131, or merely to change thedisplay on the video screen for the purpose of selecting a differenttype of presentation, or for imposing a different surgical path on thescreen, these communications are carried out through the centralprocessor unit (CPU) 140 (taken to include appropriate software 141 andfirmware 142), which controls the computer-generated images (CGI) on thescreen as well as most other functions in the system. As such, once thesurgeon/user has finally determined his selection of template, hassuperimposed that template using the computer controls 16 onto thepositioning diagnostics at the desired location where the surgery is tobe effected, and the modifications to the shape of the template havebeen effected to accommodate for the particular configuration of thepatient as observed through the video display means 27 (which includesscreen 20) and the reconstructed target cross-sections, then the systemis set to automatically fire at a discretized approximation of theconfiguration selected on the video screen 20. Discretizationtechniques, computer pattern overlay means, and the inherent CAD/CAMsoftware techniques necessary to accomplish this process are known artand, as such, are not further described. The user's control of thetemplate is thus indirect, proceeding via instructions received andstored in the computer memory, which in turn, generates, processes andstores template information as shown by control line 121.

[0114] The CPU 140 is connected to a number of other components. Forexample, it can send information to an I/O unite (not shown in FIG. 10)for record keeping. The transmissions may include, for example, patienthistory records to be printed or stored.

[0115] The CPU 140 can send control signals to a dedicated I/O boards152 which may be used for e.g., driving motors associated with thesteering Risley assembly 21, as well as for driving X-Y axis adjustmentsand other tracking functions through software included in 151.Commercially available dedicated I/O boards are capable of handling 16analog channels and three digital channels in the currently describedembodiment of the system 10. Thus, one board (in, e.g., 142) can handlediagnostic information relating to laser status, position status,tracker mirror status, and other diagnostics which may be implemented asneeded such as intraocular temperature, intraocular pressure readings,and surface wave propagation measurements to enable calculation of theYoung's modulus and other elasticity constants in an effort to determineapplicable constitutive relations. The sensors for these conditions ofthe eye are not shown in the drawings, but can be incorporated in thesystem of the invention.

[0116] In FIG. 10, the surgeon/user is indicated at 8. Interactionbetween the surgeon and the patient is mostly indirect (as shown bydashed line 5), via the instrument and system of the invention. Thus,information and data concerning the patient's tissue is fed back,indirectly, through the instrument, to the surgeon, via video display27, contained within user interface 19. The surgeon/user inputsinstructions and commands to user interface 19 and the user interfacefeeds back information to the user, principally via video screen 20.This is indicated by a line 25.

[0117] The pointing device 42 is indicated in FIG. 10 as a key link inthe surgeon's control of the user interface. It is used to control allaspects of the operation from generating templates to viewing,diagnosing and treating the target tissue.

[0118] The eye/target 3 is shown as sending information to a topographysystem 98 (comprising a light projector 95 and topographic datacollection system 77), a viewing /imaging system 86 (comprising blocks45 through 49), and to X-Y and Z position analysis tracking detectors 50and 53 contained within assemblies 85 and 84, respectively. Asrepresented in FIG. 10, the imaging/viewing system 86 comprises thevideo microscope 46, which presents the tissue video image (exemplifiedin FIGS. 12-15 discussed below), the zoom control 47, the aiming viewingmeans 48 and the focus viewing means 49. A double-ended arrow 127indicates transmission of the video information to video display means27, forming a part of the user interface 19, and resulting in live videoimages 4 on video screen 20. Control arrow 127 between the userinterface and viewing system 86 also indicates that the surgeon maycontrol the magnification of the video microscope depicted in block 46via zoom control function 47, as well as view selected aim points andbeam focus, all of which comprise parts of complete assembly 86.

[0119] The control line 123 from the user interface to themicroprocessor (which indicates the surgeon/user's selections made byinput controls other than touch screen), thus serves to representanother user input to the microprocessor 140 active when the user steersthe field of vision and the aim of the laser. Such deliberate control bythe surgeon will indirectly control the laser beam aiming and focus viathe microprocessor (along the control lines 113 and 114, as discussedbelow). User interface signals to the computer control are also used bythe CPU 140 to adjust the CGIs accordingly, reflecting precisely thedesired change in beam focus, image magnification and aim points.

[0120] The content of signals sent by the microprocessor (CPU) 140 tothe video screen (along control line 123) relate also to thecomputer-generated topographical images acquired as shown by line 101from topography system 98, and discussed further below. CPU 140 alsocontrols the display of the branching look-up tables 30 shown on screen20, as well as other pull-down menus, displays and other pertinentinformation.

[0121] In FIG. 10, information about eye 3 is shown as being sent to ablock 77 labeled Topography via control line 104. Arrow 102 indicatedthe derivation of such information from the eye via the projectionsystem 95 while the transformation and processing of said information bythe topography system 77 is represented by arrow 103. An informationcontrol line 101 indicates processing and feedback via the computercontrol assembly 16 and dedicated microprocessors contained in 150.Block 77 is taken to include the sensors, CCD cameras, such asprofilometer camera 97, optical collection assembly 94, aperture 99 andanalysis loops. As represented in FIG. 10, the functions of a dedicatedmicroprocessor and programming for this subsystem are included withinblocks 150 and 151, respectively. The derived information relating tothe topography of the eye tissues is then sent to the trackingstabilization blocks discussed next.

[0122] The X-Y position analysis and tracking system (contained withinassembly 85 and described operationally for FIG. 5) proceeds primarilythrough the tracking detectors 50 and the servo drive 5 1, but is alsounderstood to include the servo logic loops and any associated opticsrequired to steer the light emanating from the images received fromtarget/eye 3, as indicated by arrow 108, for the said purpose ofdetecting and following any movement of the patient's tissue. Thisinformation is related to the X-Y servo drive 51, via informationcontrol loop 109 which, in turn, controls the tracking mirror 72, asindicated by arrow 116. This logic sequence indicates that the detectorssubsystem, after analyzing the images and determining that a feature hasmoved, sends information or instructions to the servo drive, whichconstitutes the target tracking assembly (along with dedicatedprocessors included in 150). The information or instructions cancomprise new coordinates for the position of mirror 72. The targettracking assembly thus translates the new coordinates into instructionsfor the mirror drivers via arrow 116 to the servo mirror 72), whichinstructions may include coordinate transform information and commandsfor the tracking mirror 72 to turn to a new angle which will again becentered on the same features.

[0123] An information arrow 111, shown between the position analysistracking detectors and the computer control 16, indicates processing ofthe information and stabilization of the video images by a dedicatedmicroprocessor, contained within the units 150, shown in FIG. 10 (forsimplicity) as embedded within the central computer assembly 16.Computer processing functions relating to the X-Y tracking unit includeappropriate programming units which are able to analyze data taken bythe tracking detectors 50 and to determine form the data when featureshave moved and to relocate those features and calculate new coordinatesfor mirror position. Some of these functions were described further withreference to FIG. 5. Control arrow 117 also represents feedback from themirror assemblies as to their actual position, as well as confirmationthat the mirror was physically moved, i.e., that the instruction to themirror resulted, where indicated, in a physical displacement. If thismove does not occur, the system loops back to the target trackingassembly which sends a signal along control loop 144 to disable thelaser firing. The important control arrow 144 thus relates to thepreferred safety feature embodied within the present invention. Thetarget tracking assembly, if unable to track the moved feature to a newlocation within the time allotted (which may be as fast as a fewmilliseconds in a preferred embodiment), will send an instruction to aninternal fire control 100 to abort firing of the laser, and this commandis relayed to the laser power control via arrow 144. The automaticfiring control mechanism represented by block 100 will also interruptthe execution of the template program, vis a vis the control line 121 inFIG. 10. The interrupt preferably lasts only until the feature isrecovered via the tracking loop (discussed above), if in fact thefeature is recovered.

[0124] Examples of tracking loss not associated with the logic loop arefailure of the signal to be effected by the servo drivers, requiredmirror motion exceeding the limiting displacement of the servo drivenactuators and malfunction of the drivers or slides. Safety controlswhich shut down the operation of the system whenever tracking is lostare a feature of the present embodiment of the invention but are notfurther described as they comprise standard safety devices known in thefield.

[0125] In one embodiment of the invention, a microprocessor in block 150also controls the tracking mirror or servo mirror 72, as indicated byarrow 117. The microprocessor controls the mirror in response to inputfrom the tracking detectors 50 in conjunction with suitable programmingfirmware and software 152 and 151, respectively. Thus, once the trackingdetectors input signals to the microprocessor (via control line 111 )which indicate that the subject tissue has undergone movement, themicroprocessor handles the position analysis and the target tracking(mirror instruction) and outputs as signal in response to the results ofthe tracking to the tracking mirror 72 as indicated by line 117.

[0126] A dashed control 120 from servo tracking mirror 72 to laser aimblock 75 indicates that the laser aim is steered along with the X-Ytracking (as discussed in reference to FIG. 4). In a preferredembodiment, there may be an additional control line (not shown in FIG.1O) from the tracking mirror to the viewing assembly 86 to allow for thefact that since the laser and surgical microscope lines of sight are notcoaxial, the field of tissue being viewed and the laser are alwaysdecoupled.

[0127] It is noted that the dedicated microprocessor or other logic unithaving the capability of carrying out the logic sequence needed forpattern recognition, coordinate transform analysis and generatinginstructions to the mirror drivers to appropriately adjust the X-Yposition of the mirror 72 can also be included within the servo drive51, in which case the function of the separate control arrow 11 isobviated.

[0128] Similarly, the Z-tracking detectors 53 (contained within thedepth tracking assembly 84 discussed earlier in connection with FIG. 3)send commands regarding viewing depth and beam focus to a Z servo drivevia control loop 106, which in turn relays the information to the finalfocusing lens 17 via information loop 105. In a preferred embodiment ofthe invention, the change in orientation of the tracking mirror 72 iscommunicated to the Z-tracking compensator mirror 60 via control loop130. This feature is provided to maintain the focus of the Z-trackingsystem on the instantaneous vertex of the cornea, as discussed abovewith reference to FIG. 8.

[0129] We note that the final focusing lens also forms a part of theimaging system 86, in the sense that the surgical microscope receiveslight on a path which passes through this lens 17, and the focus of theimaging is adjustable at 48 and 49 by the surgeon/user; consequently, noseparate control line leading from the objective lens to the viewingassembly is indicated in FIG. 10.

[0130] The user interface activated laser fire control is shown by line144 with arrowhead toward block 44 representing an internal laser firecontrol mechanism which turns on the power source 44 that acts as thedriver for the therapeutic laser 87. The fire control sequence isinitiated by the surgeon/user when clicking the mouse 42 which moves acursor across the video screen. Firing can be manually interrupted bypushing the “abort” button 24, provided as an additional safety featurethat is under control of the surgeon/user as indicated in FIG. 10 bydashed line 125.

[0131] When operating, a fraction of the beam passes through a laserdiagnostic assembly 74, as shown by control line 129 which serves thepurpose of monitoring the laser pulse energy to insure it is performingto specification. The information is relayed to the central computerunit 16 to be analyzed and compared with specific parameters, asindicated byline 112.

[0132] The laser beam also passes through the steering and aimingsubassemblies shown as blocks 75 and 76 (contained within subassembly81). The steering assembly 75 includes the Risley prisms, which are notunder the direct control of the surgeon. The beam focusing assemblyincludes beam expander 22, which is likewise not under the directcontrol of the surgeon. Note that the entire beam steering, aiming andpositioning loop also includes the front objective element 17 as wasdiscussed vis-a-vis FIG. 4. So, again there is no separate controlindicated between the objective lens and the beam steering and focusingblocks 75 and 76. Instead, these subsystems are shown as receivingdirect control instructions form the central microprocessor via controllines 113 and 114 (which include indirect information relayed throughthe tracking mirror 72 and objective lens 17, both of which are adjustedvia appropriate servo drives whenever the patient's target tissuemoves).

[0133] Finally, the dashed line 5 indicates the laser beam's action onthe target, i.e., the patient; the actual laser treatment is thus onlyindirectly controlled by the surgeon/user.

[0134]FIG. 11 shows again separate functional blocks for the targetviewing assembly, the target tracking assembly, the topography assembly,the beam positioning/ aiming assembly and the fire control, all shownnow as being activated by the user interface, which is in turnmanipulated by the surgeon/user through a suitable pointing device 42also indicated in FIG. 11. The operator/user interface interaction takesplace primarily through the video screen means 20 (and associatedelements such as the pointing device 42) as indicated by control line25, while central microprocessor control of the interface is shown byline 123. The user interface 19 comprises for the most part an“intelligent” menu of options available to the surgeon, the video screen20 which displays the options in a suitable number of modules, thepointing device 42 (such as a mouse, joystick, trackball, light pen,etc.) for making selections from the menu, the fire control (or “abort”)button 24 and various other buttons and numerical displays as wereindicated in FIG. 9c in front of the surgeon/user. Aside from the safetyfeature indicators discussed previously, the trackball 42 (or otherpointing device, as mentioned above) enables the surgeon/user to controland select from among the various software options available for a givenmode of operation. Rotation of the trackball controls the position of acursor on the video screen. A button next to the ball enables specialfeatures on the screen and allows the user to superimpose the proposedtherapy on the video generated images of the target tissue. In thepresent invention, commercially available computer graphics softwarepackages form a portion of the basis for providing the surgeon/useraccess to defining surgical templates. Other buttons allow thesurgeon/user to switch from selecting previously defined templates, tomodifying or creating new templates.

[0135] With the user interface, the surgeon is able to make selectionsas to types of surgery or templates to be used in the surgery, to viewdifferent portions of the tissue, to aim the laser, including the depthat which the laser fires, and to fire the laser to execute apreprogrammed sequence of firings. It also enables the surgeon/user tointerrupt the procedure at any time. The surgeon makes his selections bymoving a cursor across a Windows menu consisting of several modules eachcontaining a number of options that can be displayed in the form of abranching look-up table 30 and pull-down menus. The cursor ismanipulated, preferably by (in order to obviate the risks of miskeyingon a keyboard) the pointing device 42 alluded to above. The symbols inthe menu will include the type of display desired for the screen asshown in the examples displayed in FIGS. 12-15; selection of templatesfrom among pre-programmed patterns for the proposed surgical procedure;other surgical parameters such as the laser pulse power level or therepetition rate of the laser beam; the beginning and ending diopterpower of the corneal “lens” or, more generally, the opticalprescription; the shape of the lesions; modifications of the templatesor creation of new templates, memory storage and retrieval ofinformation; record keeping and access to patient history files; accessto statistical information about the likely outcome of a proposedsurgical procedure; a selection of levels within the eye for whichinformation is desired for a given surgical procedure; and others.

[0136] All of the above operational functions are created throughsoftware programming, the details of which do not in themselves form apart of the invention and are within the skill of the programmer.

[0137] As shown in FIG. 11, the surgeon/user starts the procedure bygenerating a template (or a set of templates), a function indicated inblock 131. Based on a set of pre-programming patterns, the patient'soptical prescription or—in the case of controlled animal studies—actualtemplates for the proposed procedure (derived from other previoussurgeries conducted by himself or by other surgeon and stored inmemory), means are provided for the surgeon to create a new template ormodify an old template by appropriate resizing and resealing. The listof pre-stored patterns may include geometric shapes such as annuli,arcs, boxes, ellipses, radii, and others, as shown in the pull-down menu36 of FIG. 12, under the “utilities” module 31. Specific types ofoperations and/or lesions may be selected from among options storedunder the “treatment” module shown as vertical box 37 in FIG. 13. Forexample, in the case of corneal surgery, the starting point forgenerating templates for a particular eye segment may consist ofselection from among a collection of relevant lesions, such astangential (T-cut) or, for radial keratotomy, radial (2-rad, 4-rad,etc.), as illustrated in vertical box 38 of FIG. 13. Different sets ofpatterns are provided for e.g., cataract surgery, posterior eye segmentsurgery, or other forms of intervention for which the system of thepresent invention is deemed appropriate. Specific shapes of lesions cantherefore be selected by the surgeon such as, e.g., the screens as shownin FIGS. 12 and 14 for corneal surgery, or a different set of screensfor cataract surgery, or yet a different set of screens for posterioreye segment procedures. In a preferred embodiment of the display,templates are drawn on the screen in three-dimensions through selectionfrom several standard geometrical shapes as shown in FIG. 12.Alternatively, a free form option may be included to allow thesurgeon/user to draw arbitrary shapes as may be appropriate for certaintypes of surgical procedures. Selection of a treatment plane can also bedone through, e.g., an “orientation” menu, indicated in box 37 of FIG.13, under the “treatment” module. The selected patterns can then be usedas depicted or, if a closed curve is indicated, filled in automaticallyaccording to the prescribed distance between firing locations asindicated in the menu selection under e.g., the “set parameters” box 39illustrated in FIG. 14, and contained in the “treatment” module 37depicted in FIG. 13.

[0138] The patterns selected are superimposed on a grid, shown on thescreen, with spacings corresponding to appropriate dimensions within theeye. For example, in the case of corneal surgery, a 10×10 grid with 1 mmspacings would adequately describe the human cornea (which has adiameter of 12 mm). The areas between the grid points are transparent tothe treatment beam.

[0139] When pre-programmed templates of the surgical path to be followedare used, such as in controlled animal studies, the surgeon has accessto the same options as indicated above, in addition to superimposingdirectly the template on the screen over the ocular tissues.

[0140] Access to magnification is provided throughout the templateselection and diagnostics phase through a zoom option, located on thescreen. This function is within the domain of the viewing/imagingassembly and is indicated as block 138 in FIG. 11. The surgeon can thusview any desired segment of the treated area and/or the shape of theproposed lesions, at varying magnifications up to the limit imposed bythe hardware.

[0141] The first step in the surgical procedure involves patient eyediagnostics, including key topographic measurements such a provided byprofilometry, keratometry, and corneoscopy as indicated by block 132 ofFIG. 11. A “diagnostic” module may be provided in a preferred embodimentof the user interface, an example of which is shown in FIG. 15. Thismodule may comprise commands to perform various non-invasive proceduresand present the results in the form of three-dimensional graphics andrefractive power maps. Controls of the viewing system and the tools forperforming measurements may all be exercised concurrently within thismodule. Thus, profilometry measurements, which involve the topographysubassembly 98, provide the surgeon with data on the patient's cornealsurface. The procedure involves projection of a pre-selected patternunto the eye or other alternative techniques as was discussed for FIG.7.

[0142] In a preferred embodiment of the invention, the 16-spoke, 5-ringpattern shown in FIGS. 12 and 14, has been selected, although otherpatterns may be appropriate for different procedures. The reflectedimages are grabbed, digitized and spatially transformed to reproduce keysurface characteristics, which are saved as a file on a disk. Thekeratometry means reads from the file to generate a 3D surface that canbe displayed on the screen in the form of a contour map as part of thecorneoscopy routine, once the appropriate radii and planes have beenselected. An example of such a power map is also shown in FIG. 15. Inone embodiment of the software, a 75×75 matrix is used to generate thesurface projection, in the form of e.g., an equipower map 92. The 3Dpattern can be manipulated by means of a scroll bar to rotate and tiltit. It can also be displayed in the form of a color coded contour map asvisual aid to indicate feature elevation. A palette is provided in themenu under e.g., the “utilities” module to allow color selection for thedisplay.

[0143] Based upon the corneal measurements, the spatial map of therefractive power of the cornea can also be constructed. This may also beincluded in the diagnostics module, and the power map can be presentedin a separate window, if desired.

[0144] As discussed above, FIGS. 12-15 show examples of what may bedisplayed on a screen 20 of the video monitor 18. The information on thescreen 20 is intended to give the user a full range of informationregarding the three-dimensional structure or features of the particulartissues on which laser surgical procedures are to be performed. In apreferred embodiment of the user interface, some symbols are included onthe screen such a in vertical strips 31, 36, 37, 38, 39, and 40 as shownon the screens of FIGS. 12, 13, 14, and 15. These symbols comprise amenu of selections for the surgeon/user. Other display means can be alsoused to present data in a more easily understood manner to thesurgeon/user. For example, in FIG. 15, a preferred embodiment of thegraphical representation means 92 or the topographical map means 93, isshown in a super-posed manner. These can also be shown as separatewindows. The menu 40, shown in FIG. 13, may be used to generate on thevideo screen to show pertinent measurement data relating to the tissueon which surgery is to be performed. A final selection of the referencesurface at a given target depth can be made concurrently with thediagnostic routine, by entering appropriate data in box 39 of FIG. 14(which corresponds, in the example of FIG. 13, to the “set parameters”menu, shown as part of the “treatment” module 37) and observing theimmediate effect on the reconstructed corneal surface, displayed in amanner similar to the example shown in FIG. 15. This type of comeoscopydisplay provides critical aid to the surgeon in determining, e.g., thedegree of astigmatism present in the patient's tissue. In the preferredembodiment, the user will also be able to superimpose the template ofthe selected surgical path on the video microscope-generated image ofthe corneal (or other tissue).

[0145] A key step in the treatment involves selection of laser operatingparameters for the actual surgery, indicated by block 133 in FIG. 11 andillustrated in the photograph of the user interface, as depicted in box39 of FIG. 14. The principal parameters included in the treatment modulemay include the energy of the laser, the repetition rate, desiredspacing between fire points, desired lesion depth and thickness (for thesurface selected earlier), direction of treatment along the Z-axis(inward, outward), lesion radius for selected profile projections, andother pertinent parameters as may be indicated by a particular type ofsurgery to be performed. FIGS. 12 and 14 also show examples of what maybe indicated on the screen for a selected corneal lesion shape which isshown in two projections, customarily referred to as S-1(superior-inferior) and N-T (nasal-temporal). In a preferred embodimento the elements included in system 10, the maximum energy/pulse is 0.3mJ, in which case the spacing has a default value of 14 μm, asdetermined by the bubble size for that level of energy at thatparticular wavelength. These parameters are relevant to cornealprocedures; appropriate laser parameters must be selected for alternateophthalmic procedures, such as operations on the lens, for which thehardware of present invention can also be suitably modified.

[0146] The surgeon can thus use the information provided in the variouswindows to provide diagnostic information of the actual condition of thetarget tissue to the surgeon/user. Thus, the surgeon might firstestablish the pattern in the screen in plane view, observe the resultsof his selection in various perspective views, as shown in FIGS. 12 and14, wherein the proposed lesion is automatically indicated, and reflectupon the likely outcome of the surgery with the ability to edit, analter as desired, the designated template pattern prior to initiatingthe procedure.

[0147] At any point during the diagnostics and the lesion selectionphase, the user can superpose the actual laser aim points on theproposed lesion shapes and/or image of the tissue (from the videocamera) indicated on the screen through a click of the mouse, on the“show aim points” option from, e.g., the “treatment” module, box 37 inFIG. 13. This option is also activated just prior to the final step inthe procedure, which involves actual firing of the laser to perform thesurgery, as indicated by block 144 in FIG. 11.

[0148] The template-controlled laser firing must occur precisely inaccordance with the pre-selected targeting sequence. It is the trackingsystem (including diagnostic, tracking and mirror movement) which is thecritical link in this feedback loop. This function is indicated by block134 in FIG. 11. The tracking feature is automatically activated duringdiagnostic and treatment phases. As noted earlier in this disclosure, ifthe tracking subsystem fails to move the servo controlled turningmirrors to maintain the target within acceptable error tolerances, thenthe template-controlled laser firing will be disabled until the imagesare again reacquired or until the surgeon re-initiates the program.Likewise, if an obstruction (such as a blinking eyelid for ophthalmicprocedures or transient debris in industrial procedures) were tointerfere with the imaging/tracking light path (which also correspondswith the laser beam path), the template-controlled laser firing will beinterrupted until the images are reacquired and the appropriate positionin the template firing sequence is recovered. The closed loop 135indicates automatic aim point maintenance for the laser. If allconditions are met (patient ready, tracking is online, laser is armed),the surgeon may select the “start” option under the “treatment” module37 (see FIG. 13) which commences the surgery. If, at any time loss oftracking is indicated, or other, potentially unsafe conditions areencountered (such as energy deviation, per, e.g., block 136 in FIG. 11),the firing sequence is automatically immobilized through safetyinterlock features shown as block 100 in FIG. 11 (see also FIG. 10). Thesurgeon can also choose to interrupt the procedure manually by pressingon the fire control or, abort switch 24, also connected to the safetyinterlock system. In either case, the last aim point position is storedin the computer memory, along with all other pertinent data concerningthe operation. The procedure can therefore be resumed at will byclicking a “continue” option (also shown in box 37 of FIG. 13). This hasthe effect of allowing the target area to be reacquired and tracked, andthe laser will then fire according to the original pattern and sequenceselected, starting at the precise aim point location last exercisedprior to the interruption.

[0149] Upon completion of the operation, a “report” option (see, e.g.,box 37 in FIG. 13) may be provided, whereby the procedure details can besummarized and pertinent statistical information stored and displayed. A“statistical” module (not shown) may be provided as part of the software(e.g., under the “file” module) to fulfill this function.Characteristics of the treatment which may be recorded and reported mayinclude the total number of laser pulses fired, the total energydeposited into the tissue, time elapsed and other pertinent data.

[0150] A disc file input/output (1/0) module is also incorporated tosupport all the necessary exchanges with external memory devices. Thusall the information about a given surgical session can be stored forfuture analysis and/or reports, along with the values selected for allparameters, templates, and personal data. The results of theprofilometric measurements can be stored in a separate file, which maybe retrieved when needed.

[0151] Note that the techniques for obtaining mapping and profileinformation of selected surfaces within the eye in the embodiments ofthe present invention are not limited to any one specific surface. Thetechniques described herein apply to either the cornea or the iris,lens, etc. With some modification in the imaging optics, retinalprocedures may be included as well (note that the retina is a reflectingsurface in that there is an index of refraction change across thesurface. Consequently, there will be for each incident light ray areflected ray, a refracted ray, ray absorption, and scattering of light,all of which must be taken into account when selecting specific methodsfor acquiring and interpreting data).

[0152] It should also be understood that the system of the invention isuseful to the surgeon as a diagnostic and analytical tool, aside fromits uses in actual surgery. The system provides for the doctor highlystabilized images of the patient's tissue—particularly the oculartissue—not achievable with instruments prior to this invention. Thedoctor is given a display of the tissues, along with simultaneoustracking and stabilization. The invention therefore gives the doctor avery important tool in analysis and diagnosis of a patient's condition,and the invention should be understood to encompass the system asdescribed even without the surgical laser beam itself. The system, withits computer-generated images (CGIs) on the display screen as well asdirect video microscopic images displays of the patient/target, givesthe doctor a means of visualizing the eye condition, as a replacementfor the doctor's directly looking at the target tissues. TheTemplate-Controlled Surgical Laser (or, Ophthalmic Surgical Workstation)invention should be considered as including the user interface, thecomputer and memory storage device relative to creating, modifying,storing, and executing surgical template programs. This assembly isdefined in greater detail by Sklar in U.S. patent application Ser. No.475,657 (now abandoned) which is incorporated herein by reference.

[0153] The above described preferred embodiments are intended toillustrate the principles of the invention but without limiting itsscope. Other embodiments and variations to these preferred embodimentswill be apparent to those skilled in the art and may be made withoutdeparting from the essence and scope of the invention as defined in theclaims.

What is claimed is:
 1. A laser system for treating a tissue site of aneye with a laser beam, the system operated by a user, the systemcomprising: a pulsed laser generating a pulsed laser beam of, the laserbeam being deliverable to the tissue site; a sensor measuring a positionof the eye and generating a first electrical signal; a processor havinga memory and a computer program, the processor effecting an interruptionof a firing of the laser in response to the first signal.
 2. The systemof claim 1 wherein the first signal is generated in response to anobject near the eye.
 3. The system of claim 2 wherein the object nearthe eye comprises an interposing obstacle.
 4. The system of claim 3wherein the interposing obstacle comprises an eyelid.
 5. The system ofclaim 1 wherein the light energy comprises an ablative light energy anda treatment of the site comprises ablating a surface of a cornea of theeye to change a refractive power of the eye.
 6. The system of claim 5further comprising a laser delivery system for delivering the beam oflight energy to the eye.
 7. The system of claim 6 wherein the laserdelivery system comprises at least one moving part.
 8. The system ofclaim 7 wherein the interruption is generated in response to a positionof the eye.
 9. The system of claim 8 further comprising: a display forviewing the tissue site of the eye; optical path means for receiving theshort pulse laser beam and for aiming the beam at a point in X-Ydirections and focussing the beam at a depth as desired toward a target,including a front lens element from which the beam exits the opticalpath means toward the patient, beam steering means connected to theoptical path means for controlling the position at which the beam isaimed in X-Y directions, beam focussing means connected to the opticalpath means for controlling the depth at which the laser beam isfocussed, tracking means for tracking eye movements of the patientduring the progress of the surgery, including X-Y tracking means fortracking a feature of the eye in X and Y directions, and depth or Ztracking means for tracking depth movements of the eye's feature, towardand away from the workstation, and the processor connected to thetracking means for automatically shifting the optical path means as thefeature of the eye is tracked through X-Y and Z movements, so as tochange the aim and focus of the laser beam when necessary to follow suchmovements of theeye.
 10. The system of claim 1 wherein the processoreffects a continuation of the firing in response to a second signal. 11.The system of claim 10 wherein the firing of the laser is according to apredetermined sequence of laser beam pulses, and the continuation of thefiring is according to the predetermined sequence. 12 The system ofclaim 10 wherein the second signal comprises an electrical signalgenerated by the sensor.
 13. The system of claim 10 wherein the secondsignal comprises a signal generated in response to an action of theuser.
 14. A method for treating a tissue site of an eye with a laserbeam, the method comprising: delivering a pulsed beam of a light energyto the site; controlling firing of the laser with a processor; measuringa position of the eye with a sensor, the sensor generating a firstelectrical signal; and the controlling of the laser firing includinginterrupting the firing of the laser in response to the first signal.15. The method of claim 14 wherein the first signal is generated inresponse to an object near the eye.
 16. The method of claim 15 whereinthe object near the eye comprises an interposing obstacle.
 17. Themethod of claim 16 wherein the interposing obstacle comprises an eyelid.18. The method of claim 14 wherein the light energy comprises anablative change a refractive power of the eye.
 19. The method of claim18 further comprising: receiving the short pulse laser beam and aimingthe beam at a point in X-Y directions and focussing the beam at a depthwith optical means and when appropriate toward a target, through a frontlens element; controlling the position at which the beam is aimed in X-Ydirections, using a beam steering means connected to the optical means;controlling the depth at which the laser beam is focussed, with a beamfocussing means connected to the optical means; tracking eye movementsof the patient during the progress of the surgery, in X and Ydirections, with an X-Y tracking means for tracking a feature of theeye, and as to depth movements of the eye with a depth or Z trackingmeans; and automatically shifting the optical path means as the featureof the eye is tracked through X-Y and Z movements, so as to change theaim and focus of the laser beam when necessary to follow such movementsof the eye, with the aid of the processor connected to the trackingmeans.
 20. The method of claim 19 wherein the laser delivery systemcomprises at least one moving part; and a position of the part during apulse of the beam is determined by the sequence.
 21. The method of claim20 wherein the interrupting of the sequence is in response to themeasuring of the eye.
 22. The method of claim 21 further comprisingviewing a tissue site of the eye on a display.
 23. The method of claim14 wherein the step of controlling includes continuing the firing inresponse to a second signal.
 24. The method of claim 23 wherein thecontrolling of the firing of the laser is according to a predeterminedsequence of laser beam pulses, and the step of interrupting the firingcomprises interrupting the firing according to the predeterminedsequence, the step of continuing comprising continuing the firingaccording to the predetermined sequence. 25 The method of claim 23wherein the second signal comprises a signal generated by the sensor.26. The method of claim 23 wherein the second signal comprises a signalgenerated in response to an action of the user.